Semiconductor device, wafer, method for manufacturing semiconductor device, and method for manufacturing wafer

ABSTRACT

According to one embodiment, a semiconductor device includes a first layer of n-type including a nitride semiconductor, a second layer of p-type including a nitride semiconductor, a light emitting unit, and a first stacked body. The light emitting unit is provided between the first and second layers. The first stacked body is provided between the first layer and the light emitting unit. The first stacked body includes a plurality of third layers including AlGaInN, and a plurality of fourth layers alternately stacked with the third layers and including GaInN. The first stacked body has a first surface facing the light emitting unit. The first stacked body has a depression provided in the first surface. A part of the light emitting unit is embedded in a part of the depression. A part of the second layer is disposed on the part of the light emitting unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2011-202323, filed on Sep. 15,2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device,a wafer, a method for manufacturing the semiconductor device, and amethod for manufacturing the wafer.

BACKGROUND

Nitride semiconductors are used in various semiconductor devices such assemiconductor light emitting devices and HEMT (high electron mobilitytransistor) devices. However, the characteristics of such nitridesemiconductor devices are restricted by high density threadingdislocations due to lattice mismatch with the GaN crystal.

For instance, semiconductor light emitting devices based on nitridesemiconductors are expected as a phosphor-exciting light source for e.g.white LED, but have low efficiency.

Various proposals have been made to increase the efficiency of LED andother semiconductor light emitting devices based on nitridesemiconductors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a semiconductor deviceaccording to a first embodiment;

FIGS. 2A to 2D are schematic sectional views illustrating a part ofsemiconductor devices according to the first embodiment;

FIG. 3 is a schematic sectional view illustrating the semiconductordevice according to the first embodiment;

FIG. 4 is a schematic sectional view illustrating an alternativesemiconductor device according to the first embodiment;

FIG. 5 is a schematic sectional view illustrating an alternativesemiconductor device according to the first embodiment;

FIG. 6 is a schematic sectional view illustrating an alternativesemiconductor device according to the first embodiment;

FIG. 7 is a schematic sectional view illustrating a wafer according to asecond embodiment;

FIG. 8 is a flow chart illustrating a method for manufacturing asemiconductor device according to a third embodiment;

FIG. 9 is a schematic sectional view illustrating a semiconductor deviceaccording to a fourth embodiment;

FIG. 10 is a graph illustrating the characteristics of the semiconductordevice according to the fourth embodiment;

FIG. 11 is a schematic sectional view illustrating a wafer according toa fifth embodiment; and

FIG. 12 is a flow chart illustrating a method for manufacturing asemiconductor device according to a sixth embodiment.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor device includes a firstlayer of n-type including a nitride semiconductor, a second layer ofp-type including a nitride semiconductor, a light emitting unit, and afirst stacked body. The light emitting unit is provided between thefirst layer and the second layer. The light emitting unit includes abarrier layer and a well layer. The first stacked body is providedbetween the first layer and the light emitting unit. The first stackedbody includes a plurality of third layers including AlGaInN, and aplurality of fourth layers alternately stacked with the plurality ofthird layers and including GaInN. The first stacked body has a firstsurface facing the light emitting unit. The first stacked body has adepression provided in the first surface. A part of the light emittingunit is embedded in at least a part of the depression. A part of thesecond layer is disposed on the part of the light emitting unit embeddedin the at least a part of the depression.

According to another embodiment, a semiconductor device includes a firstlayer of n-type including a nitride semiconductor, a second layer ofp-type including a nitride semiconductor, a light emitting unit, a firststacked body, and a second stacked body. The light emitting unit isprovided between the first layer and the second layer. The lightemitting unit includes a barrier layer and a well layer. The firststacked body is provided between the first layer and the light emittingunit. The first stacked body includes a plurality of third layersincluding AlGaInN, and a plurality of fourth layers alternately stackedwith the plurality of third layers and including GaInN. The secondstacked body is provided between the first layer and the first stackedbody. The second stacked body includes a plurality of fifth layershaving a composition different from a composition of the third layersand including a nitride semiconductor, and a plurality of sixth layersalternately stacked with the plurality of fifth layers and includingGaInN. The second stacked body includes a first portion near the firstlayer and a second portion located between the first portion and thelight emitting unit. An In average concentration in the first portion ishigher than an In average concentration in the second portion.

According to another embodiment, a wafer includes a substrate, a firstlayer of n-type, a first stacked body, a light emitting unit, and asecond layer of p-type. The first layer of n-type is provided on thesubstrate and includes a nitride semiconductor. The first stacked bodyis provided on the first layer. The first stacked body includes aplurality of third layers including AlGaInN, and a plurality of fourthlayers alternately stacked with the plurality of third layers andincluding GaInN. The light emitting unit is provided on the firststacked body. The light emitting unit includes a plurality of barrierlayers and a well layer provided between the plurality of barrierlayers. The second layer of p-type is provided on the light emittingunit and includes a nitride semiconductor. The first stacked body has afirst surface facing of the light emitting unit. The first stacked bodyhas a depression provided in the first surface. A part of the lightemitting unit and a part of the second layer are embedded in at least apart of the depression.

According to another embodiment, a wafer includes a first layer ofn-type including a nitride semiconductor, a second layer of p-typeincluding a nitride semiconductor, a light emitting unit, a firststacked body, and a second stacked body. The light emitting unit isprovided between the first layer and the second layer. The lightemitting unit includes a plurality of barrier layers and a well layerprovided between the plurality of barrier layers. The first stacked bodyis provided between the first layer and the light emitting unit. Thefirst stacked body includes a plurality of third layers includingAlGaInN, and a plurality of fourth layers alternately stacked with theplurality of third layers and including GaInN. The second stacked bodyis provided between the first layer and the first stacked body. Thesecond stacked body includes a plurality of fifth layers having acomposition different from a composition of the third layers andincluding a nitride semiconductor, and a plurality of sixth layersalternately stacked with the plurality of fifth layers and includingGaInN. The second stacked body includes a first portion near the firstlayer and a second portion located between the first portion and thelight emitting unit. An In average concentration in the first portion ishigher than an In average concentration in the second portion.

According to another embodiment, a method is disclosed for manufacturinga semiconductor device. The method can include forming a first layer ofn-type including a nitride semiconductor on a substrate. The method caninclude forming a first stacked body by alternately stacking a pluralityof third layers including AlGaInN and a plurality of fourth layersincluding GaInN on the first layer. The method can include forming alight emitting unit including a plurality of barrier layers and a welllayer provided between the plurality of barrier layers on the firststacked body. In addition, the method can include forming a second layerof p-type including a nitride semiconductor on the light emitting unit.The first stacked body has a first surface facing the light emittingunit. The first stacked body has a depression provided in the firstsurface. The forming the light emitting unit includes embedding a partof the light emitting unit in at least a part of the depression. Theforming the second layer includes embedding a part of the second layerin at least a part of a remaining space of the depression.

According to another embodiment, a method is disclosed for manufacturinga semiconductor device. The method can include determining a crystalgrowth condition when forming a second stacked body by alternatelystacking a plurality of fifth layers including a nitride semiconductorand a plurality of sixth layers including GaInN on a first layer ofn-type including a nitride semiconductor, and forming a first stackedbody by alternately stacking a plurality of third layers having acomposition different from the fifth layers and including AlGaInN and aplurality of fourth layers including GaInN on the second stacked body.The second stacked body has a first portion and a second portion beingfarther from the first layer than the first portion. The crystal growthcondition makes an In average concentration in the first portion beinghigher than an In average concentration in the second portion. Themethod can include forming the second stacked body and the first stackedbody by using the determined crystal growth condition, forming a lightemitting unit including a barrier layer and a well layer on the firststacked body, and forming a second layer of p-type including a nitridesemiconductor on the light emitting unit.

According to another embodiment, a method is disclosed for manufacturinga wafer. The method can include forming a first layer of n-typeincluding a nitride semiconductor on a substrate. The method can includeforming a first stacked body by alternately stacking a plurality ofthird layers including AlGaInN and a plurality of fourth layersincluding GaInN on the first layer. The method can include forming alight emitting unit including a plurality of barrier layers and a welllayer provided between the plurality of barrier layers on the firststacked body. In addition, the method can include forming a second layerof p-type including a nitride semiconductor on the light emitting unit.The first stacked body has a first surface facing the light emittingunit. The first stacked body has a depression provided in the firstsurface. The forming the light emitting unit includes embedding a partof the light emitting unit in at least a part of the depression. Theforming the second layer includes embedding a part of the second layerin at least a part of a remaining space of the depression. Variousembodiments will be described hereinafter with reference to theaccompanying drawings.

The drawings are schematic or conceptual. The relationship between thethickness and the width of each portion, and the size ratio between theportions, for instance, are not necessarily identical to those inreality. Furthermore, the same portion may be shown with differentdimensions or ratios depending on the figures.

In the present specification and the drawings, components similar tothose described previously with reference to earlier figures are labeledwith the same reference numerals, and the detailed description thereofis omitted appropriately.

(First Embodiment)

The embodiment relates to a semiconductor device. The semiconductordevice according to the embodiment includes a semiconductor device suchas a semiconductor light emitting device, a semiconductor lightreceiving device, and an electron device. The semiconductor lightemitting device includes e.g. a light emitting diode (LED) and a laserdiode (LD). The semiconductor light receiving device includes e.g. aphotodiode (PD). The electron device includes e.g. a high electronmobility transistor (HEMT), a heterojunction bipolar transistor (HBT), afield effect transistor (FET), and a Schottky barrier diode (SBD).

In the following, examples in which the embodiment is applied to asemiconductor light emitting device are described.

FIG. 1 is a schematic sectional view illustrating the configuration of asemiconductor device according to the first embodiment.

As shown in FIG. 1, the semiconductor device 10 according to theembodiment includes a first layer 130, a second layer 150, a lightemitting unit 140 (functional section), and a first stacked body 210.

The first layer 130 includes a nitride semiconductor and has n-type. Thesecond layer 150 includes a nitride semiconductor and has p-type.

In this example, the first layer 130 includes an n-type confinementlayer 131 and an n-type contact layer 132. The n-type confinement layer131 is placed between the n-type contact layer 132 and the lightemitting unit 140. The n-type confinement layer 131 includes e.g. atleast one of n-type GaN and n-type AlGaN.

In this example, the second layer 150 includes a p-type confinementlayer 151 and a p-type contact layer 152. The p-type confinement layer151 is placed between the p-type contact layer 152 and the lightemitting unit 140. The p-type confinement layer 151 includes e.g. p-typeAlGaN.

The light emitting unit 140 is provided between the first layer 130 andthe second layer 150. The light emitting unit 140 includes a barrierlayer (described later) and a well layer (described later). Forinstance, a plurality of barrier layers are provided. The well layer isprovided between the plurality of barrier layers.

The first stacked body 210 is provided between the first layer 130 andthe light emitting unit 140. The first stacked body 210 includes aplurality of third layers 203 and a plurality of fourth layers 204. Theplurality of fourth layers 204 are alternately stacked with theplurality of third layers 203. The third layers 203 include e.g.AlGaInN. The plurality of fourth layers 204 include e.g. GaInN. Thethickness of each fourth layer 204 may be thinner than the thickness ofthe well layer (described later) of the light emitting unit 140.

Here, the direction from the first layer 130 toward the second layer 150is defined as Z-axis direction. For instance, the first layer 130, thefirst stacked body 210, the light emitting unit 140, and the secondlayer 150 are stacked in this order along the Z-axis direction.

In the description, the stacked state of layers includes not only thestate in which the layers are directly stacked, but also the state inwhich the layers are stacked with a different component interposedtherebetween.

The first stacked body 210 is provided on the first layer 130. The lightemitting unit 140 is provided on the first stacked body 210. The secondlayer 150 is provided on the light emitting unit 140.

In the description, the state of being provided on a layer includes notonly the state of being placed on the layer in contact therewith, butalso the state of being placed on the layer with a different componentinterposed.

In this example, the semiconductor device 10 further includes a secondstacked body 220. The second stacked body 220 is provided between thefirst layer 130 and the first stacked body 210. The second stacked body220 includes a plurality of fifth layers 205 and a plurality of sixthlayers 206. The plurality of sixth layers 206 are alternately stackedwith the plurality of fifth layers 205. The plurality of fifth layers205 have a composition different from the composition of the thirdlayers 203. The fifth layer 205 is made of e.g. GaN. The sixth layer 206includes GaInN. The thickness of the sixth layer 206 may be thinner thanthe thickness of the well layer (described later) of the light emittingunit 140.

For instance, in the semiconductor device 10, for instance, on the majorsurface of a substrate 110, a first buffer layer 121 of AlN is provided.The major surface of the substrate 110 is made of e.g. a sapphirec-plane. On the substrate 110, a second buffer layer 122 of non-dopedGaN is provided. Specifically, the first buffer layer 121 includes afirst AlN buffer layer 121 a of high carbon concentration formed on thesubstrate 110, and a second AlN buffer layer 121 b of high purity formedon the first AlN buffer layer 121 a. The carbon concentration in thefirst AlN buffer layer 121 a is higher than the carbon concentration inthe second AlN buffer layer 121 b.

On the second buffer layer 122, for instance, an n-type contact layer132 of Si-doped n-type GaN, a Si-doped n-type confinement layer 131, alight emitting unit 140, a p-type confinement layer 151 of Mg-dopedp-type AlGaN, and a p-type contact layer 152 of Mg-doped p-type GaN arestacked.

Furthermore, on the p-type contact layer 152, for instance, a p-sideelectrode 160 of Ni is provided. On the n-type contact layer 132, forinstance, an n-side electrode 170 of Al/Au stacked film is provided.

By applying voltage between the p-side electrode 160 and the n-sideelectrode 170, a current is supplied to the light emitting unit 140, andlight (emission light) is emitted from the light emitting unit 140.

FIGS. 2A to 2D are schematic sectional views illustrating a partialconfiguration of semiconductor devices according to the firstembodiment.

More specifically, FIG. 2A illustrates the configuration of the lightemitting unit 140 in the semiconductor device 10 as well assemiconductor devices 11, 12, 13, and 14 and wafers 60 and 64 describedlater. FIG. 2B illustrates the configuration of the light emitting unit140 in semiconductor devices 10 a, 11 a, 12 a, 13 a, and 14 a and wafers60 a and 64 a. FIG. 2C illustrates the configuration of the lightemitting unit 140 in semiconductor devices 10 b, 11 b, 12 b, 13 b, and14 b and wafers 60 b and 64 b described later. FIG. 2D illustrates theconfiguration of the light emitting unit 140 in semiconductor devices 10c, 11 c, 12 c, 13 c, and 14 c and wafers 60 c and 64 c described later.

As shown in FIG. 2A, in the semiconductor device 10, the light emittingunit 140 includes a plurality of barrier layers 41 (e.g., first barrierlayer BL1 and second barrier layer BL2) and a well layer 42. The welllayer 42 is provided between the plurality of barrier layers 41.

For instance, the light emitting unit 140 can have a single quantum well(SQW) structure. In this case, the light emitting unit 140 includes twobarrier layers 41 and a well layer 42 provided between the barrierlayers 41. For instance, the light emitting unit 140 can have a multiplequantum well (MQW) structure. In this case, the light emitting unit 140includes three or more barrier layers 41 and a well layer 42 providedbetween each pair of barrier layers 41.

In the example shown in FIG. 2A, the light emitting unit 140 includesn+1 barrier layers 41 and n well layers 42 (n is an integer of 1 ormore). The (i+1)-th barrier layer BL(i+1) is placed between the i-thbarrier layer BLi and the second layer 150 (i is an integer of 1 or moreand n−1 or less). The (i+1)-th well layer WL(i+1) is placed between thei-th well layer WLi and the second layer 150. The first barrier layerBL1 is provided between the first layer 130 and the first well layer WL1(i.e., between the first stacked body 210 and the first well layer WL1).The n-th well layer WLn is provided between the n-th barrier layer BLnand the (n+1)-th barrier layer BL(n+1). The (n+1)-th barrier layerBL(n+1) is provided between the n-th well layer WLn and the second layer150.

As shown in FIG. 2B, in the semiconductor device 10 a according to theembodiment, the light emitting unit 140 includes one well layer 42. Asshown in FIG. 2C, in the semiconductor device 10 b according to theembodiment, the light emitting unit 140 includes two well layers 42. Asshown in FIG. 2D, in the semiconductor device 10 c according to theembodiment, the light emitting unit 140 includes three well layers 42.The light emitting unit 140 may include four or more well layers 42.

Here, of the plurality of barrier layers 41, the barrier layer 41nearest to the second layer 150 is referred to as p-side barrier layerBLp. Furthermore, in the case where a plurality of well layers 42 areprovided, the barrier layer 41 provided between the plurality of welllayers 42 is referred to as interwell barrier layer BLI.

Of the plurality of barrier layers 41, the barrier layer 41 nearest tothe first layer 130 is the first barrier layer BL1. Part of the firststacked body 210 may serve as this layer. In other words, of theplurality of third layers 203 of the first stacked body 210, the layernearest to the light emitting unit 140 can serve as the first barrierlayer BL1.

The first barrier layer BL1 includes e.g. Al_(x1)Ga_(1-x1-y1)In_(y1)N(0≦x1<1, 0≦y1, 0<x1+y1≦1). The first barrier layer BL1 is made of e.g.Si-doped n-type AlGaInN.

The second barrier layer BL2 (and the m-th barrier layer BLm, m being aninteger of 2 or more) includes Al_(x2)Ga_(1-x2-y2)In_(y2)N (0≦x2, y2<1,0<x2+y2≦1). Here, x2 may be equal to or different from x1. Furthermore,y2 may be equal to or different from y1. In particular, it is morepreferable that x2<x1. It is more preferable that y1<y2.

The well layer 42 includes Al_(x0)Ga_(1-x0-y0)In_(y0)N (0≦x0, 0<y0,x0+y0<1, y1<y0, y2<y0). The well layer 42 includes Ga_(1-y0)In_(y0)N(0<y0≦1, y1<y0, y2<y0). Thus, the well layer 42 can include at least oneof GaInN and AlGaInN.

The well layer 42 has a thickness (length along the Z-axis direction) ofe.g. 2 nanometers (nm) or more and 9 nm or less.

The bandgap energy of the well layer 42 is smaller than the bandgapenergy of the barrier layer 41. The bandgap energy of the well layer 42is smaller than the bandgap energy in the first stacked body 210 and thebandgap energy in the second stacked body 220. This suppresses that thelight emitted in the well layer 42 is absorbed in other semiconductorlayers included in the semiconductor device 10. Thus, the light isextracted outside with high efficiency.

In the first stacked body 210, the thickness of the fourth layer 204 maybe thinner than the thickness of the well layer 42. The third layer 203may be thinner than the thickness of the second barrier layer BL2 (andthe m-th barrier layer BLm, m being an integer of 2 or more).

The lower limit of the thickness of the fourth layer 204 is determinedby the thickness such that the fourth layer 204 exhibits materialproperties of a continuous layer. The upper limit of the thickness ofthe fourth layer 204 is determined by the condition for providing adifference between the energy of the absorption edge in the fourth layer204 and the energy of the absorption edge in the well layer 42.

That is, the thickness of the fourth layer 204 is e.g. a thickness ofthree atomic layers or more. The thickness of the fourth layer 204 isset less than or equal to the thickness such that the energy of theabsorption edge in the fourth layer 204 is sufficiently larger than thatof the absorption edge of the well layer 42. Specifically, thewavelength corresponding to the energy of the absorption edge of thefourth layer 204 is set on the short wavelength side of the wavelengthat which the intensity of the emission spectrum of the well layer 42falls below half the peak value. The thickness of the well layer 42 ise.g. a thickness of four atomic layers or more.

For instance, if the same composition is applied to the fourth layer 204and the well layer 42, the fourth layer 204 can be grown under the samecondition as the well layer 42. This simplifies the process.Furthermore, before growing the well layer 42, through the growth of thefourth layer 204, preparation under the same growth condition as thewell layer 42 can be performed for a sufficient period of time. This canimprove the controllability of the well layer 42. In this case, bymaking the thickness of the fourth layer 204 thinner than that of thewell layer 42, the bandgap energy can be made larger than that of thewell layer 42. Thus, absorption loss in the fourth layer 204 can beeasily suppressed.

Alternatively, for instance, the fourth layer 204 can be made of GaInNhaving lower In concentration and larger bandgap energy than the welllayer 42. This can reduce absorption of the light emission from the welllayer 42 into the fourth layer 204. Furthermore, in this case, becauseof low absorption, the fourth layer 204 can be made thicker, and thenumber of pairs of the third layer 203 and the fourth layer 204 can beincreased.

The thickness of the third layer 203 is e.g. a thickness of three atomiclayers or more and 6 nm or less. The lower limit is the minimumthickness exhibiting characteristics similar to those of a continuouslayer. The upper limit is the thickness at which the influence ofoverlap of wavefunctions penetrated from both sides remains and causesdecrease of resistivity.

For instance, the Al composition of the third layer 203 is set similar(an Al concentration of approximately 10% or less) to that of thebarrier layer 41 (e.g., first barrier layer BL1). This can reduce theresistance of barriers against electrons in relation to the GaN layer,and can achieve high quality crystal growth.

The third layer 203 is doped with Si. The concentration of Si in thethird layer 203 is e.g. 1×10¹⁷ cm⁻³ or more and 2×10¹⁹ cm⁻³ or less. Atless than 1×10¹⁷ cm⁻³, for instance, the electrical resistance isincreased. Above 2×10¹⁹ cm⁻³, for instance, the crystallinity isdecreased.

For instance, if the same composition is applied to the third layer 203and the barrier layer 41 (e.g., first barrier layer BL1), the thirdlayer 203 can be grown under the same condition as the barrier layer 41.This simplifies the process. Furthermore, before growing the barrierlayer 41, through the growth of the third layer 203, preparation underthe same growth condition as the barrier layer 41 can be performed for asufficient period of time. This can improve the controllability of thebarrier layer 41 (e.g., first barrier layer BL1).

For instance, the barrier layer 41 has the function of confiningcarriers in the well layer 42. Conversely, the third layer 203 isexpected to have low resistance and to pass a current. Thus, by makingthe thickness of the third layer 203 thinner than the thickness of thebarrier layer 41 to reduce the resistance, the resistance of the devicecan be effectively reduced without compromising the carrier confinementeffect in the well layer 42.

In the second stacked body 220, the thickness of the sixth layer 206 maybe thinner than the thickness of the well layer 42. The fifth layer 205may be thinner than the thickness of the second barrier layer BL2 (andthe m-th barrier layer BLm, m being an integer of 2 or more).

The thickness of the sixth layer 206 is e.g. a thickness of three atomiclayers or more. The thickness of the sixth layer 206 is set less than orequal to the thickness such that the energy of the absorption edge inthe sixth layer 206 is sufficiently larger than that of the absorptionedge of the well layer 42. Specifically, the thickness of the sixthlayer 206 is set so that the wavelength corresponding to the energy ofthe absorption edge of the sixth layer 206 is set on the shortwavelength side of the wavelength at which the intensity of the emissionspectrum of the well layer 42 falls below half the peak value. Therelationship between the thickness of the sixth layer 206 and thethickness of the well layer 42 can be considered similarly to therelationship between the thickness of the fourth layer 204 and thethickness of the well layer 42. Thus, like the fourth layer 204, thethickness of the sixth layer 206 may be made thinner than that of thewell layer 42. The thickness of the sixth layer 206 is e.g. 1 nm.

The thickness of the fifth layer 205 is e.g. a thickness of three atomiclayers or more and 6 nm or less. The lower limit is the minimumthickness exhibiting characteristics similar to those of a continuouslayer. The upper limit is the thickness at which the influence ofoverlap of wavefunctions penetrated from both sides remains and causesdecrease of resistivity. The thickness of the fifth layer 205 is e.g.2.5 nm.

The fifth layer 205 is doped with e.g. Si. The concentration of Si inthe fifth layer 205 is e.g. 10×10¹⁷ cm⁻³ or more and 2×10¹⁹ cm⁻³ orless. At less than 10×10¹⁷ cm⁻³, for instance, the electrical resistanceis increased. Above 2×10¹⁹ cm⁻³, for instance, the crystallinity isdecreased. The Si concentration in the fifth layer 205 is e.g. 1.2×10¹⁸cm⁻³.

The relationship between the thickness of the fifth layer 205 and thethickness of the barrier layer 41 can be considered similarly to therelationship between the thickness of the third layer 203 and thethickness of the barrier layer 41. Thus, like the third layer 203, thethickness of the fifth layer 205 may be made thinner than that of thebarrier layer 41. The thickness of the fifth layer 205 is e.g. 2.5 nm.

The number of fifth layers 205 may be larger by one than the number ofsixth layers 206. Alternatively, the number of fifth layers 205 may besmaller by one than the number of sixth layers 206.

In the case of growing the second stacked body 220 at low temperature inconformity with the sixth layer 206, growth at decreased temperature canbe started from the sixth layer 206. If the number of sixth layers 206is increased, the growth can be started from a flatter layer. Thisenables crystal growth with particularly high quality.

In the embodiment, the number of pairs of the third layer 203 and thefourth layer 204 in the first stacked body 210 may be equal to ordifferent from the number of pairs of the fifth layer 205 and the sixthlayer 206 in the second stacked body 220.

The corresponding emission wavelength of the first stacked body 210 ispreferably 370 nm or more and 380 nm or less. The present inventors haveexperimentally confirmed by PL measurement that if the correspondingemission wavelength of the first stacked body 210 is 370 nm or more and380 nm or less, and particularly 370 nm or more and 375 nm or less, thenthe light emitting unit 140 has high light emission efficiency. Based onthis experimental result, it is considered that setting thecorresponding emission wavelength of the first stacked body 210 to thewavelength range of 370 nm or more and 380 nm or less is desirable fordevice characteristics improvement. Here, the corresponding emissionwavelength is described. The present inventors have confirmed that lightemission from the first stacked body 210 can often be observed by PLmeasurement of the wafer used for the semiconductor device of theembodiment. The peak wavelength of this emission spectrum is defined asthe corresponding emission wavelength of this semiconductor device.

In the following, example configurations of the above layers areillustrated. However, the embodiment is not limited thereto, but can bevariously modified.

The thickness of the first buffer layer 121 is e.g. approximately 2micrometers (μm). The thickness of the first AlN buffer layer 121 a ise.g. 3 nm or more and 20 nm or less. The thickness of the second AlNbuffer layer 121 b is e.g. approximately 2 μm.

The thickness of the second buffer layer 122 is e.g. approximately 2 μm.

The Si concentration in the n-type contact layer 132 is e.g. 5×10¹⁸ cm⁻³or more and 2×10¹⁹ cm⁻³ or less. The thickness of the n-type contactlayer 132 is e.g. approximately 6 μm.

The n-type confinement layer 131 is made of e.g. Si-doped n-type GaN.The Si concentration in the n-type confinement layer is e.g.approximately 2×10¹⁸ cm⁻³. The thickness of the n-type confinement layer131 is e.g. approximately 0.5 μm.

The p-type confinement layer 151 is made of e.g. Mg-doped p-typeAl_(0.15)Ga_(0.85)N. The thickness of the p-type confinement layer 151is e.g. approximately 24 nm. The Mg concentration on the light emittingunit 140 side of the p-type confinement layer 151 is set to e.g.approximately 3×10¹⁹ cm⁻³. The Mg concentration on the opposite side (inthis example, on the p-side electrode 160 side) from the light emittingunit 140 of the p-type confinement layer 151 is set to e.g. 1×10¹⁹ cm⁻³.

The Mg concentration on the p-type confinement layer 151 side of thep-type contact layer 152 is set to e.g. approximately 1×10¹⁹ cm⁻³. TheMg concentration on the opposite side (in this example, on the p-sideelectrode 160 side) from the p-type confinement layer 151 of the p-typecontact layer 152 is set to e.g. 2×10¹⁹ cm⁻³ or more and 20×10¹⁹ cm⁻³ orless.

The well layer 42 is made of e.g. GaInN as described above. Thethickness of the well layer 42 is e.g. 2 nm or more and 9 nm or less. Inparticular, the thickness of 2.6 nm or more and 7 nm or less providesgood light emission.

The light (emission light) emitted from the light emitting unit 140 ise.g. near ultraviolet light. The peak wavelength of the emission lightis e.g. 380 nm or more and 400 nm or less. However, the embodiment isnot limited thereto. The wavelength of the emission light is arbitrary.The peak wavelength of the emission light may be e.g. longer than 400 nmand 500 nm or less.

If the peak wavelength of the emission wavelength in the light emittingunit 140 is 380 nm or more, the influence of absorption by the firststacked body 210 as well as absorption by GaN with an absorption edge of365 nm can be reduced. It is considered that setting the correspondingemission wavelength of the first stacked body 210 to the wavelengthrange of 370 nm or more and 380 nm or less is desirable for devicecharacteristics improvement. Hence, the characteristics can be improvedif the emission wavelength of the light emitting unit 140 is longer than380 nm.

In the case where the peak wavelength of the emission wavelength in thelight emitting unit 140 is 400 nm or less, the thickness of the welllayer 42 is set to 4.5 nm or more and 9 nm or less. Then, for instance,good light emission is achieved. In the case where the peak wavelengthof the emission wavelength in the light emitting unit 140 is 395 nm orless, the thickness of the well layer 42 is set to 4.5 nm or more and 7nm or less. Then, good light emission is achieved. Furthermore, thecontrollability of emission wavelength and intensity was improved.

In the case where the peak wavelength of the emission wavelength in thelight emitting unit 140 is 420 nm or more and 450 nm or less, thethickness of the well layer 42 is set to 3 nm or more and 4.5 nm orless. Then, high light emission efficiency can be achieved. In the casewhere the peak wavelength is 420 nm or more and 450 nm or less, bysetting the thickness of the well layer 42 to 3.5 nm or more and 4 nm orless, the controllability of emission intensity was improved.

In a single quantum well structure in which the peak wavelength of theemission wavelength in the light emitting unit 140 is 430 nm or more and470 nm or less, high light emission efficiency was achieved in the casewhere the thickness of the well layer 42 is 3 nm or more and 3.5 nm orless. In a multiple quantum well structure in which the peak wavelengthof the emission wavelength is 430 nm or more and 470 nm or less, highlight emission efficiency was achieved in the case where the thicknessof the well layer 42 is 2.6 nm or more and 3 nm or less.

The peak wavelength of the emission light in the light emitting unit 140can be set to e.g. 470 nm or more. Light emission was achieved in thewell layer 42 having a thickness of 2 nm or more and 3.5 nm or less.

In the embodiment, a high quality base crystal can be obtained. Hence,the configuration of the embodiment is applicable to devices includingan active layer having a longer wavelength (e.g., a wavelength in the500-nm band, 600-nm band, 700-nm band, and furthermore, an arbitrarywavelength shorter than 0.75 eV, which is the absorption edge of InN).Furthermore, in the embodiment, in addition to the single quantum wellstructure and multiple quantum well structure, the light emitting unit140 can have various configurations such as at least one of the DHstructure (double heterostructure), piecewise quantum well structure,and quantum dot structure.

The well layer 42 is made of e.g. Ga_(0.85)In_(0.15)N. In this case, thethickness of the well layer 42 is set to e.g. approximately 3.3 nm.Then, the peak wavelength of light emitted from the light emitting unit140 (well layer 42) is 400 nm or more and 450 nm or less. In the casewhere the number of well layers 42 is two, particularly high efficiencyis achieved. The number of well layers 42 may also be three.

The first barrier layer BL1 is made of e.g. Si-doped n-typeAl_(0.065)Ga_(0.93)In_(0.005)N. The Si concentration in the firstbarrier layer BL1 is set to e.g. 0.3×10¹⁹ cm⁻³ or more and 2×10¹⁻⁹ cm⁻³or less. The thickness of the first barrier layer BL1 is set to e.g.approximately 10 nm or more and 25 nm or less.

The second barrier layer BL2 (and the m-th barrier layer BLm, m being aninteger of 2 or more) is made of e.g. GaInN. The thickness of the secondbarrier layer BL2 (and the m-th barrier layer BLm, m being an integer of2 or more) is set to e.g. approximately 6 nm.

Alternatively, the second barrier layer BL2 (and the m-th barrier layerBLm, m being an integer of 2 or more) is made of e.g. GaN.

In the case where a plurality of well layers 42 are provided, theinterwell barrier layer BLI is made of e.g. GaInN. The bandgap energy ofthe interwell barrier layer BLI is preferably set to less than or equalto the bandgap energy of the first barrier layer BL1 and less than orequal to the bandgap energy of the p-side barrier layer BLp.

The second barrier layer BL2 (and the m-th barrier layer BLm, m being aninteger of 2 or more) is made of e.g. Ga_(0.93)In_(0.07)N. The thicknessof the second barrier layer BL2 (and the m-th barrier layer BLm, m beingan integer of 2 or more) is e.g. larger than 2 nm and less than 9 nm.More preferably, the thickness of the second barrier layer BL2 (and them-th barrier layer BLm, m being an integer of 2 or more) is larger than2 nm and less than 5 nm.

To form a deep potential for efficiently generating ultraviolet lightemission with an emission wavelength of 380 nm or more and 400 nm orless, the Al composition in the first barrier layer BL1 and the i-thbarrier layer BLi (1<i≦n) may be set to 6% or more.

The thickness of the barrier layer 41 is set to 2 nm or more. If thethickness of the barrier layer 41 (p-side barrier layer BLp) nearest tothe second layer 150 of p-type AlGaN is thinner than 2 nm, then in theprocess for increasing the growth temperature to grow the p-type AlGaNlayer, the well layers 42 such as the n-th well layer WLn undergothermal degradation. To control the characteristics of the well layer 42including the influence of impurity diffusion, the thickness of thep-side barrier layer BLp is set to 4.5 nm or more. In particular, if thethickness of the p-side barrier layer BLp is thicker than the thicknessof the well layer 42, there is a significant effect of relaxing theinfluence of strain between the p-type AlGaN layer and the well layer42.

If the p-side barrier layer BLp is too thick, this causes the increaseof device resistance. If the barrier layers 41 other than the firstbarrier layer BL1 are too thick, this causes the increase of deviceresistance. Furthermore, carriers overflowing the well layer 42 areaccumulated and cause absorption. Conversely, if the barrier layers 41other than the p-side barrier layer BLp are too thin, the carrierconfinement to the well layer 42 is weakened, and the light emissionefficiency is decreased. To reduce this influence, the barrier layers 41other than the first barrier layer BL1 are preferably made thinner thanthe first barrier layer BL1. In particular, in a semiconductor devicewith the thickness of the p-side barrier layer BLp set to 4 nm or moreand 9 nm or less, the device can be operated with a voltage increase of10% or less of the operating voltage anticipated from the emissionwavelength. In a device with the thickness of the barrier layers 41other than the first barrier layer BL1 and the p-side barrier layer BLpset to 4 nm or more and 15 nm or less, light emission characteristicswith high efficiency were achieved.

The thickness of the first barrier layer BL1 can be set to a value inthe range of e.g. 4.5 nm or more and 30 nm or less. If the thickness ofthe first barrier layer BL1 is set to 4.5 nm or more, the intrinsicmaterial properties are developed, and the effect of suppressing holeoverflow is achieved. Furthermore, in the case where the thickness ofthe first barrier layer BL1 is 30 nm or less, high quality crystalgrowth can be performed relatively easily.

The thickness of the first to n-th barrier layers BL1-BLn is preferablythicker than that of the well layer 42. By setting the thickness of thefirst barrier layer BL1 to be thicker than the thickness of the welllayer 42, carrier supply to the well layer 42 is effectively controlled.In particular, the thickness of the first to n-th barrier layers BL1-BLnis preferably twice or more the thickness of the well layer 42. Settingthe thickness of the first to n-th barrier layers BL1-BLn to twice ormore the thickness of the well layer 42 enables carrier supply to bothsides of the first to (n−1)-th barrier layers BL1-BL(n−1). This improvesthe accuracy of carrier supply to the well layer 42.

To efficiently inject holes from the second layer 150 of p-type AlGaNinto the n-th well layer WLn, the thickness of the p-side barrier layerBLp is preferably thin except for the aforementioned condition. Thus,the thickness of the p-side barrier layer BLp may be thinner than thatof the third layer 203 of the first stacked body 210 and the fourthlayer 204 of the second stacked body 220.

The first barrier layer BL1 suppresses that, for instance, holesinjected into each well layer 42 of the light emitting unit 140 flow outto the first layer 130 side. To achieve the effect of potential blockagainst carriers, particularly including the case where there arecrystal defects and the like, the thickness of the first barrier layerBL1 is made sufficiently thick. If the thickness of the first barrierlayer BL1 is approximately 15 nm or more and 20 nm or less, a sufficienteffect is achieved. When the thickness of the first barrier layer BL1was thinner than 13 nm, decrease of yield ratio was sometimes observed.That is the increase of the ratio devices with large efficiency droop athigh injection current density. When the thickness of the first barrierlayer BL1 was thicker than 22 nm, an increase was sometimes observed inthe proportion of devices with high resistance.

The third layer 203 of the first stacked body 210 and the fifth layer205 of the second stacked body 220 are located on the opposite side ofthe first barrier layer BL1 from the light emitting unit 140. Hence, thethird layer 203 and the fifth layer 205 play a less significant rolethan the first barrier layer BL1 in suppressing the leakage of holesfrom the light emitting unit 140. On the other hand, the third layers203 and the fifth layers 205 are provided in a plurality, and hence arelikely to act as resistance of current. Thus, to decrease the drivingvoltage of the device, it is preferable to make the third layer 203 andthe fifth layer 205 as thin as possible. Hence, the thickness of thethird layer 203 and the fifth layer 205 is preferably thinner than thethickness of the first barrier layer BL1.

The thickness of the third layer 203 and the fifth layer 205 ispreferably thin to reduce electrical resistance. Thus, the bandgap ofthe first barrier layer BL1 is made larger than that of these layers toincrease the electrical resistance to reduce the hall leakage of thefirst barrier layer BL1. The relationship of the thickness of the firstbarrier layer BL1, the thickness of the third layer 203, and thethickness of the fifth layer 205 is the relationship of effectivethickness in terms of electrical resistance. For instance, at least theeffective thickness of the first barrier layer BL1 is set larger than orequal to the effective thickness of the third layer 203 and theeffective thickness of the fifth layer 205. This improves the devicecharacteristics.

The first barrier layer BL1 can be doped with Si at high concentrationto reduce the influence of the piezoelectric field applied to the welllayer 42. Thus, light emission with high efficiency can be achieved.

With regard to the relationship among the well layer 42 of the lightemitting unit 140, the GaInN layer of the fourth layer 204 of the firststacked body 210, and the GaInN layer of the sixth layer 206 of thesecond stacked body 220, the thickness of the GaInN layer is preferablythinner than the thickness of the well layer 42. Then, the opticalbandgap energy of the well layer 42 is made smaller than the opticalbandgap energy of GaInN of the fourth layer 204 and GaInN of the sixthlayer 206. This suppresses that the light emission of the well layer 42is absorbed by at least one of GaInN of the fourth layer 204 and GaInNof the sixth layer 206. The relationship in thickness among the welllayer 42, GaInN of the fourth layer 204, and GaInN of the sixth layer206 can be specified by effective thickness in terms of each opticalbandgap energy. The effective thickness of GaInN of the fourth layer 204and the effective thickness of GaInN of the sixth layer 206 arepreferably thinner than the effective thickness of the well layer 42.

In the thin film structure, the bandgap energy can be significantlyvaried simply by varying the composition to fabricate a crystal in whichthe thinner layer has smaller bandgap energy than the thicker layer.However, this causes a large difference in the In concentration ofGaInN, and also causes a large difference in material properties. Thus,high quality crystal growth is difficult in this case. Thus, it is morepreferable that, the thickness of GaInN of the fourth layer 204 and thethickness of GaInN of the sixth layer 206 be thinner than the thicknessof the well layer 42.

If the Al concentration in the first barrier layer BL1 and the i-thbarrier layer BLi (1<i≦n+1) exceeds 10%, the crystal quality isdegraded. By doping the first barrier layer BL1 and the i-th barrierlayer BLi with a small amount of In, for instance, the crystal qualitycan be improved. By setting the In concentration in the first barrierlayer BL1 and the i-th barrier layer BLi to 0.3% or more, improvement incrystal quality is observed. However, if the In concentration exceeds1.0%, the crystal quality is degraded, and the light emission efficiencyis decreased. However, in the case where the thickness of the firstbarrier layer BL1 and the i-th barrier layer BLi is thin, the Inconcentration can be increased to 2%.

The fifth layer 205 of the second stacked body 220 is made of e.g. a GaNlayer having a thickness of 2.5 nm. The sixth layer 206 is made of e.g.a Ga_(0.93)In_(0.07)N layer of 1 nm. The number of stacked layers (thenumber of pairs) of the fifth layers 205 and sixth layers 206 is e.g.16. Here, for instance, the number of fifth layers 205 may be set to 17,with the number of sixth layers 206 set to 16.

The third layer 203 of the first stacked body 210 is made of e.g. anAl_(0.07)Ga_(0.93)In_(0.01)N layer having a thickness of 2 nm. Thefourth layer 204 is made of e.g. a Ga_(0.93)In_(0.07)N layer of 1 nm.The number of stacked layers (the number of pairs) of the third layers203 and fourth layers 204 is e.g. 30.

As described later, an intermediate layer may be provided between thefirst stacked body 210 and the second stacked body 220.

FIG. 3 is a schematic sectional view illustrating the configuration ofthe semiconductor device according to the first embodiment. As shown inFIG. 3, in the semiconductor device 10 according to the embodiment, thefirst stacked body 210 has a depression 210 d. The depression 210 d isprovided in the surface 210 a on the light emitting unit 140 side of thefirst stacked body 210. That is, the first stacked body 210 has thesurface 210 a (a first surface). The first surface faces the lightemitting unit 140 a. The depression 210 d is provided in the firstsurface. The depression 210 d is set back along the direction from thesecond layer 150 toward the first layer 130 (−Z-axis direction). Part ofthe light emitting unit 140 is embedded in at least part of thedepression 210 d.

Thus, the embodiment provides a semiconductor device having highefficiency.

Furthermore, part of the second layer 150 is placed on the part of thelight emitting unit 140 embedded in the at least part of the depression210 d. Furthermore, part of the second layer 150 may be embedded in (theremaining space of) at least part of the depression 210 d.

Furthermore, for instance, the depression 210 d does not penetratethrough the first stacked body 210 along the Z-axis direction. That is,the tip 210 e of the depression 210 d is located in the first stackedbody 210. The tip 210 e of the depression 210 d is located between thesurface 210 b on the first layer 130 side of the first stacked body 210and the surface 210 a on the light emitting unit 140 side of the firststacked body 210.

Furthermore, as illustrated in FIG. 3, a dislocation 510 penetratingthrough the first layer 130, the first stacked body 210, the lightemitting unit 140, and the second layer 150 is formed. The side surface210 s of the depression 210 d surrounds the dislocation 510.

For instance, the side surface 210 s of the depression 210 d issubstantially symmetric (such as circularly symmetric, 3-fold symmetric,and 6-fold symmetric) about the extension axis of the dislocation 510.For instance, the dislocation 510 is substantially parallel to theZ-axis direction. The term “substantially symmetric” includes incompletebut generally symmetric structures.

By such configuration, the semiconductor device 10 achieves highefficiency.

The present inventors have constructed the configuration of asemiconductor device capable of emitting light with high efficiencybased on the experimental results and considerations described below.

In a configuration of a semiconductor device based on nitridesemiconductors, a stacked body with a plurality of GaInN layers stackedtherein is provided between the sapphire substrate and the lightemitting unit 140 including a well layer 42 of GaInN. The presentinventors formed a stacked body (corresponding to the second stackedbody 220) by alternately stacking a plurality of GaN layers and aplurality of GaInN layers. Then, the present inventors performedexperiments for forming a semiconductor device by forming a lightemitting unit 140 including a well layer 42 of GaInN on the stackedbody. Thus, the present inventors investigated the relationship betweenthe number of stacked layers in the stacked body and the surfaceflatness of the semiconductor device. As a result, by providing astacked body in which GaN layers and GaInN layers are alternately andrepetitively stacked, the surface flatness is improved. However, thepresent inventors have found that if the number of stacked layers isincreased, there are cases where the surface flatness is converselycompromised.

Furthermore, a stacked body (corresponding to the first stacked body210) with a plurality of AlGaInN layers and a plurality of GaInN layersalternately stacked therein was interposed between the second stackedbody 220 and the light emitting unit 140. Then, the present inventorshave found that in this configuration, there are cases where the numberof GaInN layers maintaining high surface flatness is increased.

The thickness of the GaInN layer of the well layer 42 is several nm. Itis considered that the improved surface flatness reduces the influenceof unevenness on the GaInN layer of the light emitting unit 140 and canincrease the light emission efficiency.

In the case of forming the first stacked body 210 (in which AlGaInNlayers and GaInN layers are stacked) on the second stacked body 220 (inwhich GaN layers and GaInN layers are stacked), when the number ofAlGaInN layers and GaInN layers is varied, the dependence of theflatness of the crystal surface on the number of layers behavessimilarly to the dependence of the flatness on the number of layers inthe case of providing only the second stacked body 220. However, in thecase of combining AlGaInN layers and GaInN layers, even for a largernumber of layers, the flatness of the crystal surface was improvedcompared with the case of lacking the structure of the combination ofAlGaInN layers and GaInN layers. In this case, the sharp degradation offlatness as in the stacked structure of GaInN layers and GaN layers didnot occur. Furthermore, in the case of providing the first stacked body210 on the second stacked body 220, the range of the number of layerswith improved flatness was wider than the range of the number of layerswith improved flatness in the case of providing only the second stackedbody 220. That is, it is found that the combination of AlGaInN layersand GaInN layers is particularly effective for flatness improvement.

That is, the flatness of the crystal surface can be improved in a widerrange of the number of layers by combining the first stacked body 210including a plurality of stacked AlGaInN layers and GaInN layers, andthe second stacked body 220 including a plurality of stacked GaN layersand GaInN layers.

For instance, the thickness of the AlGaInN layer was set to 2.5 nm, andthe thickness of the GaInN layer was set to 1 nm. In this case, when thenumber of AlGaInN layers and the number of GaInN layers were each 3 ormore and 25 or less, the flatness was improved. That is, if the totalthickness of GaInN layers is set to 3 nm or more and 25 nm or less, theflatness is improved, and the light emission efficiency can be improved.

Combining the first stacked body 210 and the second stacked body 220expands the range of the total thickness of the GaInN layers capable ofimproving the flatness of the crystal surface. Thus, in the range of 3nm or more and 50 nm or less, there are cases where the flatness can beimproved.

The present inventors have found that in the first stacked body 210, thestacking rate around the dislocation 510 (threading dislocation) isslowed down to form a depression structure (depression 210 d). Thisdepression 210 d is filled with e.g. AlGaN (e.g., first barrier layerBL1). Then, the depression 210 d around the dislocation 510 is filledwith that AlGaN layer and the region where AlGaInN layers and GaInNlayers thinner than those formed on the flat portion are stacked.

If the effective bandgap energy in the region where AlGaInN layers andGaInN layers thinner than those formed on the flat portion are stackedis larger than the bandgap energy of GaInN of the well layer 42, thendissipation of the injected current around the dislocation 510 withouteffectively contributing to light emission in the well layer 42 of GaInNis suppressed.

Furthermore, in the case where the light emitting unit 140 includes aplurality of well layers 42 and an interwell barrier layer BLI, it isconsidered that the aforementioned effect is further enhanced if theeffective bandgap energy in the region where AlGaInN layers and GaInNlayers thinner than those formed on the flat portion are stacked islarger than the bandgap energy of the interwell barrier layer BLI.

For instance, preferably, the tip 210 e of the depression 210 doccurring around the threading dislocation is formed in the firststacked body 210 so that a mixed region of AlGaInN layers and GaInNlayers is formed around the threading dislocation. The bandgap energy inthe region where AlGaInN layers and GaInN layers thinner than thoseformed on the flat portion are stacked is larger than the bandgap energyof stacked GaN layers and GaInN layers. By the formation of such aregion with large bandgap energy, for instance, the aforementionedeffect is efficiently achieved.

In the following, the embodiment is described in more detail. If GaN,InN, AlN, and a mixed crystal thereof are formed on the depressedsurface and made thinner than on the flat portion, then it is consideredthat In, Ga, and Al, in the increasing order of coupling to N, are moreeasily separated in this order from the crystal and contribute moresignificantly to thinning. Thus, in the slope filling the depression 210d, it is considered that the Al composition tends to increase, and theIn composition tends to decrease. In GaInN, in terms of composition aswell as in terms of thickness in view of the quantum effect, it isconsidered that the bandgap energy tends to increase. In AlGaInN, it isconsidered that the bandgap energy tends to increase in terms ofcomposition. In this case, particularly in the stacked structure ofAlGaInN and GaInN, the bandgap energy is increased. It is consideredthat the thinned stacked structure formed around the dislocation has asignificant effect of suppressing the flow of current in the dislocationand significantly contributes to increasing the (optical) output of thelight emitting device.

Thus, the semiconductor device 10 according to the embodiment provides asemiconductor device having high efficiency.

Furthermore, it is found that the characteristics of the semiconductordevice, and particularly the characteristics of the electrical junction,can be improved by providing the first stacked body 210 between thesecond stacked body 220 and the light emitting unit 140.

The second stacked body 220 includes GaN layers and GaInN layers. Thesecond stacked body 220 has e.g. a superlattice structure. The latticemismatch between the GaN layer and the GaInN layer is large, and thegrowth rate around the dislocation 510 is slow. Hence, a recess isformed around the dislocation 510. At the center of the recess, forinstance, the dislocation 510 exists. In this case, a strain is appliedthereto by the stacking of the superlattice structure. Thus, thedislocation 510 is gradually bent and directed along a directiongenerally perpendicular to the layers (Z-axis direction).

The present inventors observed this state by cross-sectional TEM.

FIG. 3 is depicted based on the cross-sectional TEM image.

The opening of the recess depends on the direction of the dislocation510. In the oblique portion of the dislocation 510, the opening of therecess is wide. As the dislocation 510 becomes vertical (parallel to theZ-axis direction), the opening of the recess becomes smaller. Thiscauses the slope (side surface) of the recess to be formed from asurface stable in terms of energy. It is considered that this results indecreasing the growth rate, decreasing the In incorporation efficiency,and enhancing the symmetry of the side surface of the recess. That is,in the portion where the opening of the recess is narrow, In is noteasily incorporated.

Thus, the In average concentration is high in the first portion (theportion on the first layer 130 side) of the second stacked body 220. Asthe second stacked body 220 grows and narrows the opening, the Inaverage concentration is gradually decreased. It is considered that whenthe shape of the depression 210 d is stabilized, the In averageconcentration becomes constant.

Such a crystal can be realized by forming a superlattice structure ofGaN and GaInN with appropriate adjustment. Primarily, the thickness andperiod are adjusted. For instance, the thickness of the GaN layer ise.g. 2.5 nm. The thickness of the GaInN layer is e.g. 1 nm. The Inconcentration is approximately 0.5%. The period (the number of GaNlayers and the number of GaInN layers) is 16.

The recess generated in the second stacked body 220 is taken over to thefirst stacked body 210 (AlGaInN layers and GaInN layers) and the lightemitting unit 140 while maintaining the shape with the dislocation 510directed in the vertical direction. The recess extends toward thesurface with the substantially vertical direction left unchanged. Theshape of the recess (depression 210 d) has a generally rotationallysymmetric structure opening toward the surface (to the direction fromthe first layer 130 toward the second layer 150). For instance, therecess is shaped like a circular cone, hexagonal pyramid, or trigonalpyramid. The axis of rotational symmetry is generally directed along thedislocation 510.

The depression 210 d formed in the first stacked body 210 is filled withpart of the light emitting unit 140. For instance, it is observed in thecross-sectional TEM image that the well layer 42 (InGaN layer) and thebarrier layer 41 (AlGaInN layer) are stacked symmetrically with respectto the dislocation 510 coinciding with the central axis of thedepression 210 d.

The thickness of the first stacked body 210 is thicker than the depth ofthe depression 210 d formed in the first stacked body 210. If thedepression 210 d penetrates through the first stacked body 210, forinstance, this causes leakage of carriers. To suppress this, theconfiguration (primarily the thickness and period) of the first stackedbody 210 is appropriately designed. For instance, the thickness of theAlGaInN layer is e.g. 2 nm. The thickness of the GaInN layer is e.g. 1nm. The period (the number of AlGaInN layers and the number of GaInNlayers) is e.g. 30.

If the dislocation 510 penetrating through the light emitting unit 140is directed vertically, the proportion of the area of the portiondisturbed by the dislocation 510 to the area of the light emitting unit140 is decreased. This increases the light emission efficiency.Furthermore, if the dislocation 510 is directed vertically, the currentbecomes less likely to flow therein, and the leakage of current issuppressed. Moreover, the In concentration around the dislocation 510 isdecreased. Thus, the bandgap energy around the dislocation 510 isincreased. This suppresses lateral current toward the dislocation 510and reduces the leakage current. Furthermore, the relative area ratio ofthe region where the crystal around the dislocation 510 is disturbed isdecreased. This improves the quality of the second layer 150 grown onthe light emitting unit 140. Furthermore, the manufacturing yield isimproved.

In forming the stacked body, if the growth rate is slowed down, theincorporation efficiency of Al (strongly coupled to nitrogen) into thecrystal surface is made higher than the incorporation efficiency of In(weakly coupled to nitrogen) and Ga (moderately coupled to nitrogen)into the crystal surface. Thus, by using the first stacked body 210based on AlGaInN layers and GaInN layers, a region with high Alcomposition is formed more easily around the dislocation 510. Thissuppresses current flow into the dislocation 510 and suppresses leakagecurrent.

In a layer with high Al concentration, the direction of the dislocation510 is easily changed from vertical. It is considered that the shape ofthe depression 210 d is stabilized by supplying In, which is weaklycoupled to nitrogen and facilitates the motion of atoms at the crystalsurface, during the formation of the AlGaInN layer.

Furthermore, by repetitively forming thin AlGaInN layers and thin GaInNlayers, the GaInN layer having high In concentration and easily assuminga thermodynamically stable state is formed before the shape of thedepression 210 d is significantly varied during the formation of theAlGaInN layer. It is considered that this stabilizes the shape of thedepression 210 d.

Thus, by providing a first stacked body 210 in which a plurality ofAlGaInN layers and a plurality of GaInN layers are alternately stacked,the dislocation 510 is formed vertically in the light emitting unit 140.This improves the efficiency.

The present inventors have also found that the configuration of thesemiconductor device 10 according to the embodiment improves theflatness of the crystal surface. By combining the second stacked body220 and the first stacked body 210, a crystal with high surface flatnesscan be formed. Thus, in this configuration, by increasing the number ofGaInN layers, the depression 210 d can be efficiently formed in thefirst stacked body 210, and a flat well layer 42 can be formed.

As described above, in the first stacked body 210, the stacking ratearound the threading dislocation (dislocation 510) is slowed down toform a depression 210 d. The depression 210 d is filled with part of thelight emitting unit 140 and part of the second layer 150. Thus, a regionwith large bandgap energy where AlGaInN layers and GaInN layers thinnerthan those formed on the flat portion are stacked is formed around thedislocation 510. This suppresses current leakage to the neighborhood ofthe dislocation, and suppresses the efficiency decrease of thesemiconductor device. Thus, light emission with high efficiency isachieved.

In the embodiment, in the case of providing a plurality of well layers42, more uniform carrier injection is achieved if the bandgap energy ofthe barrier layer 41 between the well layers 42 is made smaller than thebandgap energy of the first barrier layer BL1 (e.g., AlGaInN).

In the embodiment, the bandgap energy of the well layer 42 is smallerthan the bandgap energy of the other layers (e.g., first barrier layerBL1, GaN-containing layers, AlGaN-containing layers, first stacked body210, and second stacked body 220). This suppresses absorption of lightemission of the well layer 42 into the other layers. Furthermore,because the well layer 42 has small unevenness, the absorption edgeenergy of the well layer 42 has small fluctuation. This reduces theeffect in which light emission in one region of the well layer 42 isabsorbed in another region of the well layer 42 where the absorptionedge energy is small. Furthermore, in the case where the number of welllayers 42 is made small (e.g., 1, 2, or 3), absorption of light by otherlayers is suppressed, which would occur in the case of many (e.g., fouror more) well layers 42 having different carrier distributions and hencedifferent light emission states. By these effects, emission light isefficiently extracted outside.

In the semiconductor device 10 according to the embodiment, forinstance, the number of well layers 42 is set to 1 or more and 3 orless. This prevents nonuniformity of carriers which would occur in thecase of providing many well layers 42. Furthermore, because the numberof well layers 42 is small, a uniform well layer 42 can be formed underthe optimal fabrication condition. As a result, the light emissionefficiency in the well layer 42 can be increased. Furthermore,absorption in the well layer, which would occur in the case of many welllayers 42, is small. Hence, the light extraction efficiency can also beincreased.

For instance, in the case of one well layer 42, electrons and holes areinjected into the same well layer 42. This increases the light emissionefficiency. Furthermore, because there is no other well layer, there isno problem with the distribution of injection carrier density among thewell layers by which light emission is absorbed by the well layer havinglow injection carrier density to decrease the overall light emissionefficiency.

In the case of two well layers 42, a well layer 42 with high injectionefficiency is provided on the injection region side, and a well layer 42with high accumulation efficiency is provided on the pn junction side.This configuration is less likely to produce a well layer 42 having lowlight emission efficiency and a significant effect as an absorber, as inthe case of providing many (e.g., four or more) well layers 42.

In the case of three well layers 42, as a structure including aplurality of well layers 42, the simplest structure symmetric withrespect to electron injection and hole injection is produced. Thisconfiguration is less likely to produce a well layer 42 having low lightemission efficiency and a significant effect as an absorber, which islikely to occur in the case of providing many, such as eight or more,well layers 42.

In the semiconductor device 10 according to the embodiment, in the casewhere the number of well layers 42 is set to four or more, even if thecurrent injection density per area is increased, the carrier injectiondensity per state density is not easily increased. Hence, a high outputsemiconductor device driven by large current can be easily realized.

In a semiconductor device emitting blue light (the peak wavelength oflight emission is e.g. 450 nm or more and 480 nm or less), the Inconcentration in the well layer 42 is high. Hence, if a well layer 42having a thickness of 4.5 nm or more is formed, the strain due tolattice mismatch between the GaN layer and the well layer 42 is toolarge. Thus, the crystal quality is degraded, and the light emissionintensity is decreased. On the other hand, if the thickness of the welllayer 42 is thin, confinement of carriers to the well layer 42 is weak.Thus, in the SQW structure, it is difficult to achieve high lightemission efficiency. Consequently, the MQW structure is adopted.

In the embodiment, in the case of providing a plurality of well layers42, the bandgap energy of the interwell barrier layer BLI may be setsmaller than the bandgap energy of AlGaInN of the first barrier layerBL1. Thus, holes are uniformly injected into the well layer 42, and highlight emission efficiency can be achieved. Furthermore, in the case ofusing the first barrier layer BL1 like this, the first barrier layer BL1has at least one of higher Al concentration and lower In concentrationthan the interwell barrier layer BLI. Thus, the lattice constant of thefirst barrier layer BL1 is smaller than the lattice constant of theinterwell barrier layer BLI. Hence, the strain of the light emittingunit 140 having high In concentration and large lattice strain isrelaxed by the first barrier layer BL1 adjacent thereto. Thus, even inthe case of using a high In concentration, a good crystal is obtained.

If the bandgap energy of the p-side barrier layer BLp is made higherthan the bandgap energy of the interwell barrier layer BLI, high energyholes can be injected into the light emitting unit 140. This cansuppress nonuniformity of the hole concentration distribution betweenthe plurality of well layers 42. Thus, the light emission efficiency canbe further increased.

Thus, the semiconductor device 10 according to the embodiment provides asemiconductor device having high efficiency.

In the embodiment, by setting the thickness of the well layer 42 to 2 nmor more and 9 nm or less, high light emission efficiency and goodspectrum characteristics are achieved.

In the case where the well layer 42 is made of e.g. Ga_(0.93)In_(0.07)N,high light emission efficiency is achieved by setting the thickness ofthe well layer 42 to 4.5 nm or more and 9 nm or less.

According to the present inventors investigation, in the case where thethickness of the well layer 42 is thinner than 4.5 nm, the lightemission intensity is significantly low. The thickness larger than 9 nmresults in broadening of the light emission spectrum and significantdecrease of the light emission intensity.

In the case where the thickness of the well layer 42 is thinner than 2nm, spreading of carriers from the well layer 42 to the barrier layer(e.g., at least one of the first barrier layer BL1, the interwellbarrier layer BLI, and the p-side barrier layer BLp) is increased. It isconsidered that this causes the efficiency decrease. If the thickness ofthe well layer 42 exceeds 9 nm, the lattice mismatch between the GaNlayer (such as the second buffer layer 122, the n-type contact layer132, and the n-type confinement layer 131) and the well layer 42 isincreased, and the strain applied to the crystal becomes too large. Itis presumed that this decreases the crystal quality.

In particular, in the case where the thickness of the well layer 42 is 3nm or more and 4.5 nm or less, by increasing the number of well layers42, the light emission intensity was successfully made equal to orhigher than that of the configuration of a single well layer 42. On theother hand, if the thickness of the well layer 42 is set to 7 nm ormore, the emission wavelength is significantly restricted, and it isdifficult to fabricate a well layer 42 with a wavelength longer than 450nm. If the thickness of the well layer 42 is 7 nm or less, spectrumbroadening does not substantially occur. Thus, even in the case wherethere are fluctuations in the shape and composition of the crystal, itis presumed that no strain-induced degradation in crystallinity occurssubstantially in the entire region (e.g., the entire region of the welllayer 42).

The light (emission light) emitted from the light emitting unit 140 isnot limited to this wavelength. The wavelength can be set to variousvalues as in the above description of the embodiment. The light emittingunit 140 can be variously configured as in the above description of theembodiment.

In the semiconductor device 10 according to the embodiment, decreasingthe number of wells can solve the problems of carrier nonuniformity andreabsorption in many well layers 42 as described above. Furthermore, asa result of further investigation on the configuration of thesemiconductor device 10 according to the embodiment, it has been foundthat in addition to the aforementioned effect, there is an additionaleffect of increasing the light emission efficiency in terms of crystalquality. That is, in the embodiment, by decreasing the number of welllayers 42, each layer can be optimized so as to maximize the crystalquality of the well layer 42. Conversely, in a structure with many welllayers 42 stacked therein, many well layers 42 with high strain arestacked to grow a crystal. This causes accumulation of strain with thegrowth. Thus, it is difficult to perform crystal growth of all the welllayers 42 under the same growth condition. Hence, the crystalcharacteristics are varied for each well layer 42.

In the following, an example method for manufacturing the semiconductordevice 10 according to the embodiment is described.

For instance, by using the metal organic chemical vapor depositionmethod, on a substrate 110 having a surface made of a sapphire c-plane,an AlN layer is formed as a first buffer layer 121 with a thickness ofapproximately 2 μm. Specifically, a first AlN buffer layer 121 a of highcarbon concentration (the carbon concentration is e.g. 3×10¹⁸ cm⁻³ ormore and 5×10²⁰ cm⁻³ or less) is formed with 3 nm or more and 20 nm orless. Further thereon, a second AlN buffer layer 121 b of high purity(the carbon concentration is 1×10¹⁶ cm⁻³ or more and 3×10¹⁸ cm⁻³ orless) is formed with 2 μm. Then, further thereon, a non-doped GaN layeris formed as a second buffer layer 122 (lattice relaxation layer) with athickness of 2 μm.

Then, a Si-doped n-type GaN layer with a Si concentration of 5×10¹⁸ cm⁻³or more and 2×10¹⁹ cm⁻³ or less is formed as an n-type contact layer 132with a thickness of 6 μm. Furthermore, a Si-doped n-type GaN layer witha Si concentration of 2×10¹⁸ cm⁻³ is formed as an n-type confinementlayer 131 with a thickness of 0.5 μm. More preferably, the Siconcentration in the n-type contact layer 132 is set to 1×10¹⁹ cm⁻³ ormore and 2×10¹⁹ cm⁻³ or less.

Further thereon, a second stacked body 220 is formed. For instance, GaNlayers of 2.5 nm and GaInN layers of 1 nm are alternately stacked. Thethickness of the GaN layer is larger than or equal to the thickness ofthe GaInN layer. Preferably, the thickness of the GaN layer is 7 nm orless. More preferably, the thickness of the GaN layer is 3 nm or less.The thickness of the GaInN layer is thinner than that of the well layer42. The GaN layer is doped with e.g. Si. In the second stacked body 220,the number of GaN layers and the number of GaInN layers are 12 or moreand 20 or less. If the number is less than 12, for instance, the effectof improving the flatness of the surface is small. If the number exceeds30, dislocations are easily introduced into the crystal.

On the second stacked body 220, a first stacked body 210 is formed. Forinstance, GaInN layers and AlGaInN layers are alternately stacked. Thethickness of the GaInN layer is thinner than the thickness of the welllayer 42. The thickness of the AlGaInN layer is 7 nm or less. Morepreferably, the thickness of the AlGaInN layer is 3 nm or less. In thefirst stacked body 210, the number of AlGaInN layers and the number ofGaInN layers are 16 or more and 40 or less. Preferably, the totalthickness of the plurality of GaInN layers is thicker than 22.5 nm andthinner than 40 nm. More preferably, the total thickness of the firststacked body 210 is thicker than 70 nm and thinner than 120 nm.

Further thereon, a Si-doped n-type Al_(0.065)Ga_(0.93)In_(0.005)N layeris formed as a first barrier layer BL1 with a thickness of 13.5 nm and aSi concentration of 0.5×10¹⁹ cm⁻³ or more and 2×10¹⁹ cm⁻³ or less.Further thereon, a Ga_(0.85)In_(0.15)N layer is formed as a first welllayer 42 with a thickness of 3.5 nm. Further thereon, aGa_(0.99)In_(0.01)N layer is formed as an interwell barrier layer BLIwith a thickness of 3 nm. Further thereon, a Ga_(0.85)In_(0.15)N layeris formed as a second well layer 42 with a thickness of 3.5 nm. Furtherthereon, a GaN layer is formed as a barrier layer 41 (p-side barrierlayer BLp) with a thickness of 6 nm. Thus, a light emitting unit 140including two well layers 42 is formed.

Further thereon, a Mg-doped p-type Al_(0.15)Ga_(0.85)N layer (the Mgconcentration is 1.8×10¹⁹ cm⁻³ on the light emitting unit 140 side and1×10¹⁹ cm⁻³ on the opposite side from the light emitting unit 140) isformed as a p-type confinement layer 151 with a thickness of 24 nm.Further thereon, a Mg-doped p-type GaN layer (the Mg concentration is1×10¹⁹ cm⁻³ on the p-type confinement layer 151 side and 5×10¹⁹ cm⁻³ ormore and 9×10¹⁹ cm⁻³ or less on the opposite side from the p-typeconfinement layer 151) is formed as a p-type contact layer 152. The Alconcentration in the p-type confinement layer 151 is e.g. 0.13 or moreand 0.28 or less. In particular, if the Al concentration is set to 0.13or more and 0.16 or less, high quality crystal is easily obtained.Because AlGaN with excessively large bandgap energy is not used, thedevice resistance can be decreased.

The semiconductor layer stacked body including the above semiconductorlayers is provided with electrodes by e.g. the method illustrated below.

In a partial region of the semiconductor layer stacked body, the secondlayer 150 and the light emitting unit 140 are removed by dry etchingusing a mask until the n-type contact layer 132 is exposed at thesurface. Then, entirely on the semiconductor layer stacked bodyincluding the exposed surface of the first layer 130, a SiO₂ layer isformed with a thickness of 400 nm by using a thermal CVD (chemical vapordeposition) apparatus. This SiO₂ layer is not shown in FIG. 1 and thelike.

To form a p-side electrode 160, a patterned resist for resist lift-offis formed on the semiconductor layer stacked body. Then, the SiO₂ layeron the p-type contact layer 152 is removed by ammonium fluoridetreatment. On this region where the SiO₂ layer is removed, for instance,by using a vacuum evaporation apparatus, reflective and conductive Ag isformed as a p-side electrode 160 with a thickness of 200 nm and sinteredfor one minute in a nitrogen atmosphere at 350° C.

To form an n-side electrode 170, a patterned resist for resist lift-offis formed on the semiconductor layer stacked body. The SiO₂ layer on theexposed n-type contact layer 132 is removed by ammonium fluoridetreatment. On this region where the SiO₂ layer is removed, for instance,a stacked film of Ti layer/Pt layer/Au layer is formed with a thicknessof 500 nm. Thus, the n-side electrode 170 is formed.

The n-side electrode 170 can be made of e.g. a silver alloy (e.g.,including Pd at approximately 1%). In this case, to improve ohmiccontact, for instance, the n-type contact layer 132 is formed in atwo-layer structure. Specifically, as an electrode formation portion, ahigh concentration layer having a Si concentration of 1.5×10¹⁹ cm⁻³ ormore and 3×10¹⁹ cm⁻³ or less is grown with a thickness of approximately0.3 μm. This can suppress reliability decrease due to Si segregation.

Next, the rear surface of the substrate 110 (the surface on the oppositeside from the first buffer layer 121) is polished. The substrate 110 andthe semiconductor layer stacked body are cut by e.g. cleavage or diamondblade cutting. Thus, a singulated LED device, i.e., the semiconductordevice 10 according to the embodiment, is fabricated. The semiconductordevice 10 has a width of e.g. 400 μm and a thickness of e.g. 100 μm.

The peak wavelength of light emission in the semiconductor device 10thus fabricated is 440 nm or more and 450 nm or less. The embodiment isnot limited thereto. By controlling at least one of the In concentrationand the Al concentration of the well layer 42, light emission with apeak wavelength of 380 nm or more and 780 nm or less can be obtained. Inparticular, in the range of 380 nm or more and 560 nm or less, goodlight emission is achieved. Furthermore, in the range of 385 nm or moreand 460 nm or less, the degree of freedom in the configuration ofvarious layers included in the semiconductor device 10 is increased.Thus, a semiconductor device with particularly high efficiency is easilyachieved.

The method for forming the semiconductor layers included in thesemiconductor device 10 according to the embodiment can be based on e.g.the metal organic chemical vapor deposition method and the molecularbeam epitaxy method. However, in the embodiment, the method for formingthe semiconductor layers is arbitrary.

The substrate 110 is made of e.g. sapphire, SiC, GaN, GaAs, and Si.However, in the embodiment, the substrate 110 is arbitrary. Thesubstrate 110 may be removed after growth of the semiconductor layers.

The semiconductor device 10 according to the embodiment achieves highefficiency light emission by taking advantage of low defect crystal. Tothis end, the semiconductor device 10 is based on the configuration forincreasing the efficiency of the light emitting unit 140 itself and theconfiguration for facilitating the use of a thick p-type confinementlayer 151 having high Al concentration to suppress the overflow ofelectrons from the light emitting unit 140.

In the following, examples of each layer included in the semiconductordevice 10 according to the embodiment are described.

The first AlN buffer layer 121 a of high carbon concentration serves torelax the difference in crystal type from the substrate 110. Inparticular, the first AlN buffer layer 121 a reduces screw dislocations.Furthermore, by the second AlN buffer layer 121 b of high purity, thesurface is flattened at the atomic level. This reduces crystal defectsin the non-doped GaN buffer layer (second buffer layer 122) grownthereon. To this end, the thickness of the second AlN buffer layer 121 bof high purity is preferably thicker than 1 μm. To preventstrain-induced formation of high density dislocations, the thickness ofthe second AlN buffer layer 121 b of high purity is preferably 4 μm orless.

The first buffer layer 121 can be made of AlN as described above.However, the embodiment is not limited thereto. For instance,Al_(α2)Ga_(1-α2)N (0.8≦α2≦1) can also be used. In this case, the waferwarpage can be compensated by adjusting the Al concentration.

The second buffer layer 122 (lattice relaxation layer) serves for defectreduction and strain relaxation by three-dimensional island growth onthe first buffer layer 121. To flatten the growth surface, the averagethickness of the second buffer layer 122 (lattice relaxation layer) ispreferably set to 0.6 μm or more. In view of reproducibility and warpagereduction, the thickness of the second buffer layer 122 (latticerelaxation layer) is preferably 0.8 μm or more and 2 μm or less.

By adopting these buffer layers, the dislocation density can be reducedto 1/10 or less compared with conventional low temperature growth bufferlayers. This enables crystal growth at such high growth temperature andhigh ratio of group V raw material to group III raw material that areotherwise difficult to adopt due to abnormal growth. Thus, generation ofpoint defects is suppressed. This enables high concentration doping ofthe AlGaN layer and the barrier layer 41 (such as the first barrierlayer BL1) with high Al composition.

In the case where the substrate is made of Si, the first AlN bufferlayer 121 a serves to relax the difference in crystal type from thesubstrate 110. In particular, the first AlN buffer layer 121 a reducesscrew dislocations. The second AlN buffer layer 121 b of high purity isprovided as necessary, and may be omitted as the case may be. The secondAlN buffer layer 121 b reduces crystal defects in the non-doped GaNbuffer layer (second buffer layer 122) grown thereon. The thickness ofthe first AlN buffer layer 121 a is preferably 6 nm or more, and morepreferably 10 nm or more. At a thickness of 6 nm or more, the effect ofprotecting the substrate surface is achieved. At a thickness of 10 nm ormore, the effect of suppressing dislocations is enhanced. To preventstrain-induced warpage, the thickness of the second AlN buffer layer 121b of high purity is preferably 4 μm or less.

Also in the case where the substrate is made of Si, the first bufferlayer 121 can be made of AlN as described above. However, the embodimentis not limited thereto. For instance, Al_(α2)Ga_(1-α2)N (0.8≦α2≦1) canbe used. In this case, the wafer warpage can be compensated by adjustingthe Al composition.

As described above, the first barrier layer BL1 includes e.g. a Si-dopedquaternary mixed crystal of AlGaInN (the Al concentration is 6% or moreand 10% or less, and the In concentration is 0.3% or more and 1.0% orless). The other barrier layers 41 (interwell barrier layer BLI andp-side barrier layer BLp) include e.g. a quaternary mixed crystal ofAlGaInN (the Al composition is 6% or more and 10% or less, and the Inconcentration is 0.3% or more and 1.0% or less), where Si doping isarbitrary. The well layer 42 includes e.g. In_(0.05)Ga_(0.95)N (the Inconcentration can be appropriately varied in the range of 4% or more and10% or less).

To produce ultraviolet light emission with high efficiency at anemission wavelength of 380 nm or more and 400 nm or less, the Alconcentration in the first barrier layer BL1 is set to 6% or more toform a deep potential.

The composition of the first barrier layer BL1 can be appropriatelychanged. For instance, the first barrier layer BL1 can be made ofAlGaInN with Al concentration lower than 6%. The first barrier layer BL1can be made of GaInN having lower In concentration than the well layer42.

The composition of the barrier layers 41 other than the first barrierlayer BL1 can also be appropriately changed. Like the first barrierlayer BL1, these barrier layers 41 can be made of AlGaInN with Alconcentration lower than 6% or GaN. These barrier layers 41 can be madeof GaInN having lower In concentration than the well layer 42.

More preferably, the barrier layers 41 other than the first barrierlayer BL1 are made of a crystal having lower Al concentration or higherIn concentration than the first barrier layer BL1. Unlike the firstbarrier layer BL1, the barrier layers 41 other than the first barrierlayer BL1 are formed on the well layer 42 of GaInN. Thus, by formingthese barrier layers 41 from a material having similar materialproperties to the well layer 42 of GaInN, high quality crystal growth atlower temperature is enabled. This can suppress degradation of the GaInNlayer during crystal growth due primarily to the influence of heat.Furthermore, the difference in bandgap energy between the barrier layer41 and the well layer 42 is reduced. This can increase uniformity of thecarrier distribution, and can increase the utilization efficiency ofcarriers. Furthermore, the influence of electrical resistance resultingfrom the difference in bandgap energy between the barrier layer 41 andthe well layer 42 can be reduced. Thus, the operating voltage of thesemiconductor device can be reduced.

The In concentration of the well layer 42 may be lower or higher thanthe foregoing. For instance, a lower In concentration of the well layer42 enables light emission at a wavelength nearer to 365 nm. Forinstance, for light emission in the wavelength band of 400 nm or moreand 440 nm or less, good light emission is achieved if the Inconcentration of the well layer 42 is set to 0.2 or more and 0.3 orless. For instance, for light emission in the wavelength band of 440 nmor more and 460 nm or less, the In concentration of the well layer 42may be set to 0.3 or more and 0.4 or less. For instance, for lightemission in the wavelength band of 460 nm or more and 500 nm or less,the In concentration of the well layer 42 may be set to 0.3 or more and0.5 or less. To achieve light emission at longer wavelength, the Inconcentration of the well layer 42 may be appropriately increased in therange of 1 or less.

The thickness of the p-side barrier layer BLp is set to e.g. 2 nm ormore. Setting the thickness of the p-side barrier layer BLp to 2 nm ormore suppresses e.g. the phenomenon in which the well layer 42 isdegraded during increasing the growth temperature to grow the secondlayer 150 after growing the p-side barrier layer BLp. For instance, ifthe thickness of the p-side barrier layer BLp is thinner than 3 nm, thenfor instance, the emission wavelength of the well layer 42 may be variedunder the influence of the p-type AlGaN layer. If the thickness of thep-side barrier layer BLp is set to 4.5 nm or more, there is asignificant effect of controlling the characteristics variation of thewell layer 42 including the influence of impurity diffusion. If thethickness of the p-side barrier layer BLp is thicker than the thicknessof the well layer 42, there is a significant effect of relaxing theinfluence of the strain between the AlGaN layer and the well layer 42.If the p-side barrier layer BLp is too thick, the device resistance maybe increased. Furthermore, if the p-side barrier layer BLp is too thick,for instance, carriers overflowing the well layer 42 are accumulated andcause absorption. To reduce this influence, the p-side barrier layer BLpis preferably made thinner than the first barrier layer BL1. In asemiconductor device with the thickness of the p-side barrier layer BLpset to 9 nm or less, the device was successfully operated with a voltageincrease of 10% or less of the operating voltage anticipated from theemission wavelength.

The thickness of the first barrier layer BL1 is set to a value in therange of e.g. 4.5 nm or more and 30 nm or less. If the thickness of thefirst barrier layer BL1 is set to 4.5 nm or more, the intrinsic materialproperties are developed, and the effect of suppressing hole overflow isachieved. Furthermore, in the case where the thickness of the firstbarrier layer BL1 is 30 nm or less, high quality crystal growth can beperformed relatively easily. The thickness of the first barrier layerBL1 is preferably thicker than that of the well layer 42. By setting thethickness of the first barrier layer BL1 to be thicker than thethickness of the well layer 42, carrier supply to the well layer 42 iseffectively controlled. In particular, the thickness of the firstbarrier layer BL1 is preferably twice or more the thickness of the welllayer 42. Setting the thickness of the first barrier layer BL1 to twiceor more the thickness of the well layer 42 enables carrier supply toboth sides of the first barrier layer BL1. This improves the accuracy ofcarrier supply to the well layer 42. As described above, the firstbarrier layer BL1 can be doped with Si at high concentration to reducethe influence of the piezoelectric field applied to the well layer 42.Thus, light emission with high efficiency can be achieved.

If the Al concentration in the barrier layer 41 exceeds 10%, the crystalquality is degraded. By doping the barrier layer 41 with a small amountof In, for instance, the crystal quality is improved. By setting the Inconcentration in the barrier layer 41 to 0.3% or more, the effect ofimproving the crystal quality is observed. If the In concentrationexceeds 1.0%, the crystal quality is degraded, and the light emissionefficiency is decreased. However, in the case where the thickness isthin, the In concentration can be increased to 2%.

For instance, in the embodiment, in the case where the thickness of thefirst barrier layer BL1 is 15 nm or more, the In concentration islimited up to approximately 1%. However, if the first barrier layer BL1is thinned to 7 nm, then even if the In concentration is set to 2%, thecrystal is not degraded, and intense light emission is achieved.

An example technique for growing the first barrier layer BL1 isdescribed. It is difficult to grow a layer of quaternary mixed crystalAlGaInN with high crystal quality. Furthermore, the crystal doped withSi at high concentration is prone to degradation. By optimizing theconfiguration and growth condition of the LED device, the presentinventors successfully increased the In concentration of the barrierlayer BL1 made of AlGaInN without degrading the crystal quality.

For instance, as described above, in the embodiment, if the thickness ofthe first barrier layer BL1 exceeds 15 nm, the In concentration islimited up to approximately 1%. However, if the first barrier layer BL1is thinned to 7 nm, then even if the In concentration is set to 2%, thecrystal is not degraded, and intense light emission is achieved.

Increasing the In concentration improves the steepness of the interfacewith the well layer 42 of GaInN and improves the crystallinity of thewell layer 42. As a result, the first barrier layer BL1 of AlGaInN canbe doped with Si at high concentration.

Furthermore, by thinning the first barrier layer BL1 having high Siconcentration, the first barrier layer BL1 can be doped with Si athigher concentration.

The Al concentration of the first barrier layer BL1 can be set higherthan the Al concentration of the p-side barrier layer BLp. Thisincreases the bandgap energy of the first barrier layer BL1. Thus, theconfinement effect for holes is increased. This reduces leakage ofcurrent at the high injection current, and can increase the opticaloutput. For electrons, the p-type confinement layer 151 (p-type AlGaNlayer) serves as a barrier. Thus, the Al concentration of the p-sidebarrier layer BLp is set sufficiently lower than that of the p-typeconfinement layer 151.

For instance, the Al concentration of the first barrier layer BL1 can beset to 8% or more, and the Al concentration of the p-side barrier layerBLp can be set to 0%. In this case, the first barrier layer BL1 is grownat high temperature. Then, by decreasing the temperature to a lowergrowth temperature, the well layer 42 and the p-side barrier layer BLpmay be grown.

The interwell barrier layer BLI may be made of GaN or GaInN. Forinstance, the first barrier layer BL1 with high Al concentration isgrown at high temperature. The well layer 42 and the interwell barrierlayer BLI are grown at low temperature. The p-side barrier layer BLpwith low Al concentration is grown at low temperature. Thus, forinstance, a well layer 42 with high In concentration can be grown withgood characteristics. Here, after the p-side barrier layer BLp is grownto a thickness for protecting the surface of the well layer 42, thep-side barrier layer BLp may be grown at increased temperature.

For instance, the first barrier layer BL1 may be formed in a two-layerstructure by combining an AlGaN layer having high Al concentration andan AlGaInN layer having low Al concentration. For instance, this AlGaNlayer can suppress overflow of holes, and the AlGaInN layer can improvethe characteristics of the crystal surface. Thus, the well layer 42 canbe formed on the crystal surface with improved characteristics. In thiscase, the AlGaN layer and part of the AlGaInN layer may be grown at hightemperature, and the rest of the AlGaInN layer may be grown at the sametemperature as the well layer 42. By using such a method, a high qualityAlGaN crystal can be grown at high temperature, and the well layer 42can be grown at a temperature suitable for the well layer 42.

Such temperature change requires a large amount of time and decreasesthe process efficiency. However, in a configuration in which the lightemitting unit 140 includes a small number of well layers 42 (e.g., theconfiguration including three or less well layers 42), the decrease ofprocess efficiency can be suppressed.

For instance, in the case where the number of well layers 42 is three(e.g., semiconductor device 10 c), for instance, the In concentrationand the Ga concentration in the well layer 42 are e.g. 0.12 and 0.88,respectively. Thus, for instance, the light emitting unit 140 emits bluelight having a peak wavelength in the wavelength region of approximately400 nm. Also in this semiconductor device, the bandgap energy of thecladding layer is higher than the bandgap energy of the well layer 42.

FIG. 4 is a schematic sectional view illustrating the configuration ofan alternative semiconductor device according to the first embodiment.As shown in FIG. 4, in the semiconductor device 11 (and semiconductordevices 11 a-11 c) according to the embodiment, an intermediate layer181 is provided between the first stacked body 210 and the secondstacked body 220.

In the semiconductor device 11, on the second stacked body 220, forinstance, a GaN layer having a thickness of 2.5 nm is formed as anintermediate layer 181 by the metal organic chemical vapor depositionmethod or MOCVD method at 800-900° C. Then, on the intermediate layer181, the first stacked body 210 is formed.

The intermediate layer 181 can be made of at least one of GaN, GaInN,AlGaN, AlGaIn, and AlN. The thickness of the intermediate layer 181 ispreferably thinner than the thickness of the light emitting unit 140(the total thickness of the light emitting unit 140). If theintermediate layer 181 is thinner than the light emitting unit 140, theeffect of the strain of the first stacked body 210 can be transmittednot only to the light emitting unit 140 but also to the second stackedbody 220. The effect of the strain of the second stacked body 220 isstrongly received by the first stacked body 210. Thus, an interactioneffectively occurs therebetween. The intermediate layer 181 is providedas necessary, and can be omitted as the case may be.

FIG. 5 is a schematic sectional view illustrating the configuration ofan alternative semiconductor device according to the first embodiment.As shown in FIG. 5, in the alternative semiconductor device 12 (andsemiconductor devices 12 a-12 c) according to the embodiment, a firstmetal layer 455 is provided between a conductive substrate 460 and thep-side electrode 160. A second metal layer 465 is provided between theconductive substrate 460 and the first metal layer 455.

The semiconductor device 12 (12 a-12 c) includes a low impurityconcentration semiconductor layer 135. The n-type contact layer 132 isplaced between the low impurity concentration semiconductor layer 135and the second stacked body 220 (between the low impurity concentrationsemiconductor layer 135 and the light emitting unit 140). The n-typeconfinement layer 131 is placed between the n-type contact layer 132 andthe second stacked body 220.

The impurity concentration in the low impurity concentrationsemiconductor layer 135 is lower than the impurity concentration in then-type contact layer 132. The low impurity concentration semiconductorlayer 135 is made of e.g. a non-doped GaN layer. As the low impurityconcentration semiconductor layer 135, the second buffer layer 122(lattice relaxation layer) described above can be used.

The low impurity concentration semiconductor layer 135 is provided withan opening 138. The opening 138 exposes part of the n-type contact layer132. From the major surface 135 a of the low impurity concentrationsemiconductor layer 135 on the opposite side from the n-type contactlayer 132, the opening 138 extends to the n-type contact layer 132. Thatis, the bottom of the opening 138 extends to the n-type contact layer132.

The n-side electrode 170 is provided so as to cover the n-type contactlayer 132 exposed in the opening 138 and part of the low impurityconcentration semiconductor layer 135.

The major surface 135 a of the low impurity concentration semiconductorlayer 135 not covered with the n-side electrode 170 is provided with arough surface portion 137 including an unevenness 137 p.

The semiconductor device 12 (12 a-12 c) is fabricated by e.g. thefollowing method. For instance, on a substrate 110 made of sapphire,crystal layers of a first buffer layer 121, a second buffer layer 122(constituting a low impurity concentration semiconductor layer 135), ann-type contact layer 132, an n-type confinement layer 131, a secondstacked body 220, a first stacked body 210, a light emitting unit 140, ap-type confinement layer 151, and a p-type contact layer 152 are formedto form a crystal stacked body 180.

A p-side electrode 160 is formed on the p-type contact layer 152 of thecrystal stacked body 180. Then, the crystal stacked body 180 is bondedto a conductive substrate 460. Then, the substrate 110 and the firstbuffer layer 121 are removed. Furthermore, an n-side electrode 170 isformed on the exposed crystal layer (n-type contact layer 132). A roughsurface portion 137 (i.e., unevenness 137 p) is formed on the lowimpurity concentration semiconductor layer 135. Thus, the semiconductordevice 12 is obtained.

Also in this case, a depression 210 d is provided in the surface 210 aon the light emitting unit 140 side of the first stacked body 210. Partof the light emitting unit 140 is embedded in at least part of thedepression 210 d. Thus, the embodiment provides a semiconductor devicehaving high efficiency. For instance, part of the second layer 150 isplaced on the part of the light emitting unit 140 embedded in at leastpart of the depression 210 d. Furthermore, part of the second layer 150may be embedded in (the remaining space of) at least part of thedepression 210 d.

In the semiconductor device 12, for instance, the size of the unevenness137 p is set larger than the wavelength of emission light emitted fromthe light emitting unit 140. Specifically, the size of the unevenness137 p is set larger than the wavelength in the low impurityconcentration semiconductor layer 135 of emission light emitted from thelight emitting unit 140. Thus, the optical path is changed in the roughsurface portion 137 provided with the unevenness 137 p. This increasesthe light extraction efficiency. Thus, a semiconductor device havinghigher efficiency is obtained.

FIG. 6 is a schematic sectional view illustrating the configuration ofan alternative semiconductor device according to the first embodiment.As shown in FIG. 6, the alternative semiconductor device 13 (andsemiconductor devices 13 a-13 c) according to the embodiment isdifferent from the semiconductor device 12 (and semiconductor devices 12a-12 c) in that an intermediate layer 181 is provided between the firststacked body 210 and the second stacked body 220. This configurationalso provides a semiconductor device having high efficiency.

(Second Embodiment)

FIG. 7 is a schematic sectional view illustrating the configuration of awafer according to a second embodiment.

As shown in FIG. 7, the wafer 60 (wafer 60 a-60 c) according to theembodiment includes a substrate 110, a first layer 130, a first stackedbody 210, a light emitting unit 140, and a second layer.

The first layer 130 is provided on the substrate 110. The first layer130 includes a nitride semiconductor and has n-type. The first stackedbody 210 is provided on the first layer 130. The first stacked body 210includes a plurality of third layers 203 including AlGaInN, and aplurality of fourth layers alternately stacked with the plurality ofthird layers 203 and including GaInN.

The light emitting unit 140 is provided on the first stacked body 210.The light emitting unit 140 includes a plurality of barrier layers 41and a well layer 42 provided between the plurality of barrier layers 41.The second layer 150 is provided on the light emitting unit 140. Thesecond layer 150 includes a nitride semiconductor and has p-type.

The first stacked body 210 includes a depression 210 d provided in thesurface 210 a on the light emitting unit 140 side of the first stackedbody 210. Part of the light emitting unit 140 is embedded in at leastpart of the depression 210 d (see FIG. 3). For instance, part of thesecond layer 150 is placed on the part of the light emitting unit 140embedded in at least part of the depression 210 d. Furthermore, part ofthe second layer 150 may be embedded in (the remaining space of) atleast part of the depression 210 d.

Thus, the embodiment can provide a wafer having high efficiency.

As described with reference to FIG. 3, also in the wafer 60 (60 a-60 c),the depression 210 d does not penetrate through the first stacked body210. Furthermore, a dislocation 510 penetrating through the first layer130, the first stacked body 210, the light emitting unit 140, and thesecond layer 150 is formed. The side surface 210 s of the depression 210d surrounds the dislocation 510.

As illustrated in FIG. 7, the wafer 60 (60 a-60 c) further includes asecond stacked body 220. The second stacked body 220 is provided betweenthe first layer 130 and the first stacked body 210. The second stackedbody 220 includes a plurality of fifth layers 205 and a plurality ofsixth layers 206. The plurality of fifth layers 205 have a compositiondifferent from the composition of the third layers 203 and include anitride semiconductor. The plurality of sixth layers 206 are alternatelystacked with the plurality of fifth layers 205. Each sixth layer 206 hasa thickness thinner than the thickness of the well layer 42 and includesGaInN. The fifth layer 205 includes e.g. GaN. The thickness of each ofthe plurality of fifth layers 205 is thinner than the thickness of eachof the plurality of barrier layers 41.

The thickness of each fourth layer 204 of the first stacked body 210 isthinner than the thickness of the well layer 42. Also in this case, thewafer 60 (60 a-60 c) can further include an intermediate layer 181. Theintermediate layer 181 is provided between the first stacked body 210and the second stacked body 220. The intermediate layer 181 is thinnerthan the thickness of the light emitting unit 140.

In the wafer 60 (60 a-60 c), the well layer 42 includes e.g. at leastone of GaInN and AlGaInN. Of the plurality of barrier layers 41, thefirst barrier layer BL1 is the nearest to the first stacked body 210.The first barrier layer BL1 includes AlGaInN.

The wafer 60 (60 a-60 c) can include a first buffer layer 121 providedbetween the substrate 110 and the first layer 130, and a second bufferlayer 122 provided between the first buffer layer 121 and the firstlayer 130. The first buffer layer 121 can include a first AlN bufferlayer 121 a provided between the substrate 110 and the second bufferlayer 122, and a second AlN buffer layer 121 b provided between thefirst AlN buffer layer 121 a and the second buffer layer 122.

(Third Embodiment)

FIG. 8 is a flow chart illustrating a method for manufacturing asemiconductor device according to a third embodiment.

As shown in FIG. 8, in the method for manufacturing a wafer according tothe embodiment, a first layer 130 of n-type including a nitridesemiconductor is formed on a substrate 110 (step S102). As necessary,before step S102, a buffer layer (such as the first buffer layer 121 andthe second buffer layer 122 described above) is formed (step S101).

Then, on the first layer 130, a plurality of third layers 203 includingAlGaInN and a plurality of fourth layers 204 including GaInN arealternately stacked to form a first stacked body 210 (step S104). Asnecessary, before step S104, on the first layer 130, fifth layers 205and a plurality of sixth layers 206 are alternately stacked to form asecond stacked body 220 (step S103). The fifth layer 205 has acomposition different from the composition of the third layer 203 andincludes a nitride semiconductor. Each sixth layer 206 has a thicknessthinner than the thickness of the well layer 42 and includes GaInN.

Then, on the first stacked body 210, a light emitting unit 140 is formed(step S105). The light emitting unit 140 includes a plurality of barrierlayers 41 and a well layer 42 provided between the plurality of barrierlayers 41. Furthermore, on the light emitting unit 140, a second layer150 of p-type including a nitride semiconductor is formed (step S106).Furthermore, as necessary, after forming the second layer 150, the uppersurface of the second layer 150 is bonded to a bonding substrate (e.g.,conductive substrate). Then, the substrate 110 is removed (step S107).

The first stacked body 210 includes a depression 210 d provided in thesurface on the light emitting unit 140 side of the first stacked body210. The above formation of the light emitting unit 140 includesembedding part of the light emitting unit 140 in at least part of thedepression 210 d. The above formation of the second layer 150 includesembedding part of the second layer 150 in at least part of the remainingspace of the depression 210 d.

Thus, a semiconductor device with high efficiency can be manufactured.

By performing the above steps S101-S106, a wafer with high efficiencycan be manufactured.

(Fourth Embodiment)

The semiconductor device according to the embodiment includes asemiconductor device such as a semiconductor light emitting device, asemiconductor light receiving device, and an electronic device. In thefollowing, an example of applying the embodiment to a semiconductorlight emitting device is described.

FIG. 9 is a schematic sectional view illustrating the configuration of asemiconductor device according to the fourth embodiment.

As shown in FIG. 9, the semiconductor device 14 according to theembodiment includes a first layer 130, a second layer 150, a lightemitting unit 140 (functional section), a first stacked body 210, and asecond stacked body 220. The first layer 130, the second layer 150, thelight emitting unit 140, the first stacked body 210, and the secondstacked body 220 can be based on the configuration (including materials)described with reference to the first to third embodiments, and hencethe description thereof is omitted. In this example, an intermediatelayer 181 is provided between the first stacked body 210 and the secondstacked body 220.

FIG. 10 is a graph illustrating the characteristics of the semiconductordevice according to the fourth embodiment.

More specifically, FIG. 10 illustrates the characteristics for theconcentration of In in the semiconductor device 14. This figure shows anexample result of SIMS analysis of the semiconductor device 14. Thehorizontal axis of FIG. 10 represents position Dz (nm) in the depthdirection. The vertical axis represents secondary ion intensity I(In)for In (counts/s, counts per second).

As shown in FIG. 10, the concentration of In in the second stacked body220 is not constant. The average In composition in the portion on thefirst layer 130 side of the second stacked body 220 is higher than thatin the portion on the first stacked body 210 of the second stacked body220. The average In concentration in the second stacked body 220gradually decreases from the first layer 130 toward the first stackedbody 210. Here, the average In concentration is the average of the Inconcentrations in the fifth layers 205 and the sixth layers 206.

Thus, the second stacked body 220 includes a first portion 220 a nearthe first layer 130 and a second portion 220 b located between the firstportion 220 a and the light emitting unit 140. The average concentrationof In in the first portion 220 a is higher than the averageconcentration of In in the second portion 220 b.

On the other hand, the In average concentration in the first stackedbody 210 is substantially constant. Thus, the variation along the Z-axisdirection of the In average concentration in the first stacked body 210is smaller than the variation along the Z-axis direction of the Inaverage concentration in the second stacked body 220.

The formation of the above distribution of the In concentration in thesecond stacked body 220 is attributable to the influence of dislocations510.

The second stacked body 220 includes GaN layers and GaInN layers. Thesecond stacked body 220 has e.g. a superlattice structure. The latticemismatch between the GaN layer and the GaInN layer is large, and thegrowth rate around the dislocation 510 is slow. Hence, a recess isformed around the dislocation 510. At the center of the recess, forinstance, the dislocation 510 exists. In this case, a strain is appliedthereto by the stacking of the superlattice structure. Thus, thedislocation 510 is gradually bent and directed along a directiongenerally perpendicular to the layers (Z-axis direction).

In the semiconductor device 14, a recess similar to that illustrated inthe schematic view illustrated in FIG. 3 is formed. The opening of therecess depends on the direction of the dislocation 510. In the obliqueportion of the dislocation 510, the opening of the recess is wide. Asthe dislocation 510 becomes vertical (parallel to the Z-axis direction),the opening of the recess becomes smaller. This causes the slope (sidesurface) of the recess to be formed from a surface stable in terms ofenergy. It is considered that this results in decreasing the growthrate, decreasing the In incorporation efficiency, and enhancing thesymmetry of the side surface of the recess. That is, in the portionwhere the opening of the recess is wide, In is easily incorporated.

Thus, the In average concentration is high in the first portion 220 a(the portion on the first layer 130 side) of the second stacked body220. As the second stacked body 220 grows and the opening is narrowed,the In average concentration is gradually decreased. It is consideredthat when the shape of the depression 210 d is stabilized, the Inaverage concentration becomes constant.

As shown in FIG. 9, in the semiconductor device 14, a first metal layer455 is provided between a conductive substrate 460 and the p-sideelectrode 160. A second metal layer 465 is provided between theconductive substrate 460 and the first metal layer 455. Furthermore, anintermediate layer 181 is provided between the first stacked body 210and the second stacked body 220.

The semiconductor device 14 includes a low impurity concentrationsemiconductor layer 135. The n-type contact layer 132 is placed betweenthe low impurity concentration semiconductor layer 135 and the secondstacked body 220. The n-type confinement layer 131 is placed between then-type contact layer 132 and the second stacked body 220.

The impurity concentration in the low impurity concentrationsemiconductor layer 135 is lower than the impurity concentration in then-type contact layer 132. The low impurity concentration semiconductorlayer 135 is made of a non-doped GaN layer. As the low impurityconcentration semiconductor layer 135, the second buffer layer 122(lattice relaxation layer) described above is used.

The low impurity concentration semiconductor layer 135 is provided withan opening 138. The opening 138 exposes part of the n-type contact layer132. From the major surface 135 a of the low impurity concentrationsemiconductor layer 135 on the opposite side from the n-type contactlayer 132, the opening 138 extends to the n-type contact layer 132. Thatis, the bottom of the opening 138 extends to the n-type contact layer132.

The n-side electrode 170 is provided so as to cover the n-type contactlayer 132 exposed in the opening 138 and part of the low impurityconcentration semiconductor layer 135.

The major surface 135 a of the low impurity concentration semiconductorlayer 135 not covered with the n-side electrode 170 is provided with arough surface portion 137 including an unevenness 137 p.

The present inventors fabricated the semiconductor device 14 accordingto the embodiment and evaluated its characteristics. The semiconductordevice 14 was fabricated as follows.

On a sapphire substrate (not shown), an AlN layer having a thickness of2 μm was formed as a first buffer layer 121 by the MOCVD method atapproximately 1300° C. Further thereon, a GaN layer having a thicknessof 2 μm was formed as a second buffer 122 by the MOCVD method atapproximately 1200° C.

Further thereon, a GaN layer (n-type contact layer 132) having athickness of 4 μm and a Si concentration of 0.2×10¹⁹-1.5×10¹⁹ cm⁻³ wasformed by the MOCVD method at 1050-1200° C. Further thereon, an n-GaNlayer (n-type confinement layer 131) having a thickness of 0.5 μm and aSi concentration of 2×10¹⁷-5×10¹⁸ cm⁻³ was formed by the MOCVD method at1050-1200° C.

Further thereon, GaN layers (fifth layers 205) having a thickness of 2.5nm and doped with Si at 8×10¹⁸ cm⁻³ and sixth layers 206 ofGa_(0.93)In_(0.07)N having a thickness of 1 nm were alternately formed12-20 layers by the MOCVD method at 800-900° C. Thus, a second stackedbody 220 is formed.

Further thereon, a GaN layer (intermediate layer 181) having a thicknessof 2.5 nm was formed by the MOCVD method at 800-900° C.

Further thereon, Al_(0.07)Ga_(0.925)In_(0.005)N layers (third layers203) having a thickness of 2 nm and doped with Si at 8×10¹⁸ cm⁻³ andGa_(0.93)In_(0.07)N layers (fourth layers 204) having a thickness of 1nm were alternately formed 26-34 layers by the MOCVD method at 800-900°C. Thus, a first stacked body 210 is formed.

Further thereon, an Al_(0.07)Ga_(0.925)In_(0.005)N layer (first barrierlayer BL1: barrier layer 41) having a thickness of 13.5 nm and dopedwith Si at 4×10¹⁸-16×10¹⁸ cm⁻³ was formed by the MOCVD method atapproximately 800-900° C. Further thereon, a Ga_(0.93)In_(0.07)N layer(well layer 42) having a thickness of 7 nm was formed by the MOCVDmethod at approximately 800-900° C. Further thereon, anAl_(0.07)Ga_(0.925)In_(0.005)N layer (second barrier layer BL2: barrierlayer 41) having a thickness of 4-12 nm was formed by the MOCVD methodat approximately 800-900° C.

Further thereon, a Mg-doped p-Al_(0.2)Ga_(0.8)N layer (p-typeconfinement layer 151) having a thickness of 24 nm was formed by theMOCVD method at approximately 950-1100° C.

Further thereon, a p-GaN layer (p-type contact layer 152) having athickness of 0.3 μm was formed by the MOCVD method at 950-1100° C.Further thereon, a p-side electrode 160 was formed. Further thereon, afirst metal layer 455 was formed.

A conductive substrate 460 including a second metal layer 465 wasprepared. The first metal layer 455 was bonded to the second metal layer465. Subsequently, the sapphire substrate was removed by the laserlift-off method. An unevenness structure was formed by etching on thesurface of the exposed n-GaN layer (low impurity concentrationsemiconductor layer 135). Furthermore, by evaporation andlithograph-based patterning, an n-side electrode 170 having a prescribedshape was formed. The pattern of the n-side electrode 170 as viewedalong the Z-axis has a cross shape. The cross shape includes aperipheral portion along the periphery of the n-type contact layer 132,a first extending portion passing through the center in the X-axis ofthe n-type contact layer 132 and extending along the Y-axis, and asecond extending portion passing through the center in the Y-axis of then-type contact layer 132 and extending along the X-axis.

Subsequently, by dividing the workpiece into individual devices, thesemiconductor device 14 is obtained. In the semiconductor device 14, thelength along the X-axis is approximately 1 mm (millimeter), and thelength along the Y-axis is approximately 1 mm.

In the above semiconductor device 14, the intermediate layer 181 can beomitted. The intermediate layer 181 can be made of at least one of GaN,GaInN, AlGaN, AlGaIn, and AlN. The thickness of the intermediate layer181 is preferably thinner than the thickness of the light emitting unit140. If the intermediate layer 181 is thinner than the light emittingunit 140, the effect of the strain of the first stacked body 210 can betransmitted not only to the light emitting unit 140 but also to thesecond stacked body 220. The effect of the strain of the second stackedbody 220 is strongly received by the first stacked body 210. Thus, aninteraction effectively occurs therebetween.

In the semiconductor device 14 according to the embodiment, the lightemission efficiency was nearly constant up to a driving current of 350mA. At that driving current, an output of 0.6 W was obtained.

In a semiconductor device similar in configuration to the embodiment, ifthe average In concentration in the second stacked body 220 continuouslydecreased and failed to form a region with a constant composition, or ifthe average In concentration was not constant also in the first stackedbody 210, then the light emission efficiency decreased with the increaseof injection current density. The optical output at a driving current of350 mA was 0.55 W or less.

In the embodiment, the crystal (second stacked body 220) having the Incomposition distribution described above can be fabricated by adjustingthe superlattice structure of GaN and GaInN. Primarily, the thicknessand period are adjusted. For instance, the thickness of the GaN layer ise.g. 2.5 nm. The thickness of the GaInN layer is e.g. 1 nm. The Inconcentration is approximately 0.5%. The period (the number of GaNlayers and the number of GaInN layers) is 12-27. For instance, morepreferably, the period is 16-20.

By growing a second stacked body 220 having an average In compositionprofile as described above and growing thereon a first stacked body 210having an average In composition profile as described above, asemiconductor light emitting device with high efficiency can be formed.It is presumed that the possibility of this formation can be attributedto the following mechanism.

A recess is formed around the dislocation 510. The recess is taken overto the first stacked body 210 (AlGaInN layers and GaInN layers) and thelight emitting unit 140 while maintaining the shape with the dislocation510 directed in the generally vertical direction. It is considered thatthe recess extends toward the surface with the substantially verticaldirection left unchanged. The shape of the recess (depression 210 d) isopened toward the surface (to the direction from the first layer 130toward the second layer 150). It is presumed that the recess assumes agenerally axisymmetric shape (such as a circular cone, trigonal pyramid,and hexagonal pyramid) with respect to the dislocation.

The depression 210 d formed in the first stacked body 210 is filled withpart of the light emitting unit 140. For instance, it can be observed inthe cross-sectional TEM image that the well layer 42 (InGaN layer) andthe barrier layer 41 (AlGaInN layer) are stacked symmetrically withrespect to the dislocation 510 coinciding with the central axis of thedepression 210 d.

The thickness of the first stacked body 210 is thicker than the depth ofthe depression 210 d formed in the first stacked body 210. If thedepression 210 d penetrates through the first stacked body 210, forinstance, this causes leakage of carriers. To suppress this, theconfiguration (primarily the thickness and period) of the first stackedbody 210 is appropriately designed. For instance, the thickness of theAlGaInN layer is e.g. 2 nm. The thickness of the GaInN layer is e.g. 1nm. The period (the number of AlGaInN layers and the number of GaInNlayers) is e.g. 30.

If the dislocation 510 penetrating through the light emitting unit 140is directed vertically, the proportion of the area of the portiondisturbed by the dislocation 510 to the area of the light emitting unit140 is decreased. This increases the light emission efficiency.Furthermore, if the dislocation 510 is directed vertically, the currentbecomes less likely to flow therein, and the leakage of current issuppressed. Moreover, the In concentration around the dislocation 510 isdecreased. Thus, the bandgap energy around the dislocation 510 isincreased. This suppresses lateral current toward the dislocation 510and reduces the leakage current. Furthermore, the relative area ratio ofthe region where the crystal around the dislocation 510 is disturbed isdecreased. This improves the quality of the second layer 150 grown onthe light emitting unit 140. Furthermore, the manufacturing yield isimproved.

In forming the stacked body, if the growth rate is slowed down, theincorporation efficiency of Al (strongly coupled to nitrogen) into thecrystal surface is made higher than the incorporation efficiency of In(weakly coupled to nitrogen) and Ga (moderately coupled to nitrogen)into the crystal surface. Thus, by using the first stacked body 210based on AlGaInN layers and GaInN layers, a region with high Alcomposition is formed more easily around the dislocation 510. Thissuppresses current flow into the dislocation 510 and suppresses leakagecurrent.

In a layer with high Al concentration, the direction of the dislocation510 is easily changed from vertical. It is considered that the shape ofthe depression 210 d is stabilized by supplying In, which is weaklycoupled to nitrogen and facilitates the motion of atoms at the crystalsurface, during the formation of the AlGaInN layer.

Furthermore, by repetitively forming thin AlGaInN layers and thin GaInNlayers, the GaInN layer having high In concentration and easily assuminga thermodynamically stable state is formed before the shape of thedepression 210 d is significantly varied during the formation of theAlGaInN layer. It is considered that this stabilizes the shape of thedepression 210 d.

Thus, by providing a first stacked body 210 in which a plurality ofAlGaInN layers and a plurality of GaInN layers are alternately stacked,the dislocation 510 is formed vertically in the light emitting unit 140.This improves the efficiency.

In the semiconductor device 14 (and 14 a-14 c) according to theembodiment, the light emitting unit 140 can have various configurations,compositions, and emission wavelengths described with reference to theother embodiments.

(Fifth Embodiment)

FIG. 11 is a schematic sectional view illustrating the configuration ofa wafer according to a fifth embodiment.

As shown in FIG. 11, the wafer 64 (and 64 a-64 c) according to theembodiment includes a first layer 130, a second layer 150, a lightemitting unit 140, a first stacked body 210, and a second stacked body220. The first layer 130 includes a nitride semiconductor and hasn-type. The second layer 150 includes a nitride semiconductor and hasp-type. The light emitting unit 140 is provided between the first layer130 and the second layer 150. The light emitting unit 140 includes abarrier layer 41 and a well layer 42. For instance, a plurality ofbarrier layers 41 are provided. The well layer 42 is provided betweenthe plurality of barrier layers 41.

The first stacked body 210 is provided between the first layer 130 andthe light emitting unit 140. The first stacked body 210 includes aplurality of third layers 203 including AlGaInN, and a plurality offourth layers 204 alternately stacked with the plurality of third layersand including GaInN.

The second stacked body 220 is provided between the first layer 130 andthe first stacked body 210. The second stacked body 220 includes aplurality of fifth layers 205 and a plurality of sixth layers 206. Theplurality of fifth layers 205 have a composition different from thecomposition of the third layers 203 and include a nitride semiconductor.The plurality of sixth layers 206 are alternately stacked with theplurality of fifth layers 205 and include GaInN.

As illustrated in FIG. 10, the second stacked body 220 includes a firstportion 220 a near the first layer 130 and a second portion 220 blocated between the first portion 220 a and the light emitting unit 140.The In average concentration in the first portion 220 a is higher thanthe In average concentration in the second portion 220 b.

Thus, the embodiment can provide a wafer having high efficiency.

(Sixth Embodiment)

FIG. 12 is a flow chart illustrating a method for manufacturing asemiconductor device according to a sixth embodiment.

As shown in FIG. 12, in the method for manufacturing a semiconductordevice according to the embodiment, the crystal growth condition isdetermined (step S210). Then, by using the determined crystal growthcondition, a second stacked body 220, a first stacked body 210, a lightemitting unit 140, and a second layer 150 are formed (step S220).

For instance, on a first layer 130 of n-type including a nitridesemiconductor, a plurality of fifth layers 205 including a nitridesemiconductor and a plurality of sixth layers 206 including GaInN arealternately stacked to form a second stacked body 220. Then, on thesecond stacked body 220, a plurality of third layers 203 having acomposition different from that of the fifth layer 205 and includingAlGaInN, and a plurality of fourth layers 204 including GaInN arealternately stacked to form a first stacked body 210 (step S211).

Then, composition analysis of In in the second stacked body 220 isperformed (step S212).

The second stacked body 220 is assumed to include a first portion 220 anear the first layer 130 and a second portion 220 b farther from thefirst layer 130 than the first portion 220 a. From the result of thecomposition analysis, it is determined whether the In compositionprofile of the second stacked body 220 satisfies the condition that theIn average concentration in the first portion 220 a is higher than theIn average concentration in the second portion 220 b (step S213). If theresult of this determination is NO, the condition (the conditionincluding at least one of the crystal growth condition and the waferstructure) is changed (step S214). Then, the process returns to stepS211. The process is repeated until the result of the determinationbecomes YES.

On the other hand, if the result of the composition analysis is YES (ifthe In composition profile of the second stacked body 220 satisfies thecondition that the In average concentration in the first portion 220 ais higher than the In average concentration in the second portion 220b), the crystal growth condition is determined (step S210). Thus, thecrystal growth condition is determined so that the In averageconcentration in the first portion 220 a of the second stacked body 220near the first layer 130 is higher than the In average concentration inthe second portion 220 b of the second stacked body 220 which is fartherfrom the first layer 130 than the first portion 220 a.

Then, by using the determined crystal growth condition, a second stackedbody 220 and a first stacked body 210 are formed. On the first stackedbody 210, a light emitting unit 140 including a barrier layer 41 and awell layer 42 is formed. On the light emitting unit 140, a second layer150 of p-type including a nitride semiconductor is formed (step S220).Thus, the semiconductor device is formed.

This manufacturing method can provide a method for manufacturing asemiconductor device having high efficiency.

For instance, on a substrate 110, a first layer 130 of n-type includinga nitride semiconductor is formed. On the first layer 130, a secondstacked body 220 is formed. On the second stacked body 220, a firststacked body 210 is formed.

Then, on the first stacked body 210, a light emitting unit 140 includinga barrier layer 41 and a well layer 42 is formed. On the light emittingunit 140, a second layer 150 of p-type including a nitride semiconductoris formed.

Next, for instance, by SIMS, the In composition profile of the firststacked body 210 and the In composition profile of the second stackedbody 220 are measured.

Then, it is determined whether a prescribed average In compositionprofile has been obtained. The prescribed average In composition profileis defined as follows. In the second stacked body 220, there are aregion where the average In concentration is high on the first layer 130side and decreases on the functional region side (light emitting unit140 side), and a region where the average In concentration is nearlyconstant. In the first stacked body 210, the average In concentration isnearly constant. If the prescribed average In concentration profile hasbeen obtained, the crystal growth condition and the wafer structure arefinalized. If the intended profile has not been obtained, the crystalgrowth condition is modified. Then, the process from step S211 isperformed again. If the prescribed average In concentration profile isobtained, crystal growth is performed by using the finalized crystalgrowth condition and wafer structure. Thus, a wafer enabling fabricationof a high output semiconductor device can be fabricated. Furthermore, byusing this wafer, the device production process is performed tofabricate a semiconductor device. Thus, a semiconductor device with highefficiency can be manufactured.

The high efficiency of the semiconductor device according to the aboveembodiments is attributable to the following point, for instance. Theportion around the dislocation is filled with the stacked structure ofAlGaInN and GaInN having a larger bandgap than that of the flat portion.Thus, the active region and the region for injecting a current thereinare effectively separated from the portion around the dislocation.

In one embodiment, for instance, a first stacked body 210 is formed on aGaN layer. In the first stacked body 210, a plurality of layersincluding AlGaInN and a plurality of layers including GaInN arealternately stacked. A functional region (functional section) is formedthereon. A structure for current injection or current extraction for thefunctional region is provided. A depression is formed in the surface ofthe first stacked body 210. For instance, in this structure, thethickness of the functional region or the peripheral portion of thedepression is thinned in the depression.

For instance, the semiconductor device according to the embodimentincludes a first layer including a nitride semiconductor, a firststacked body provided on the first layer, and a functional sectionprovided on the first stacked body and including a nitridesemiconductor. The first stacked body includes a plurality of thirdlayers including AlGaInN and a plurality of fourth layers alternatelystacked with the plurality of third layers and including GaInN. Thefirst stacked body includes a depression provided in the surface on thefunctional section side of the first stacked body. Part of the lightemitting unit is embedded in at least part of the depression.

In one embodiment, for instance, on a GaN layer, a second stacked body220 is formed. In the second stacked body 220, a plurality of layershaving a composition different from AlGaInN and including a nitridesemiconductor, and a plurality of layers including GaInN are alternatelystacked. A first stacked body 210 is formed thereon. In the firststacked body 210, a plurality of layers including AlGaInN and aplurality of layers including GaInN are alternately stacked. Afunctional region (functional section) is formed thereon. A structurefor current injection or current extraction for the functional region isprovided. The following structure is provided. In the second stackedbody 220, there are a region where the average In concentration is highon the GaN layer side and decreases on the functional region side, and aregion where the average In composition is nearly constant. In the firststacked body 210, the average In concentration is nearly constant.

For instance, the semiconductor device according to the embodimentincludes a first layer including a nitride semiconductor, a firststacked body provided on the first layer, a second stacked body providedbetween the first layer and the first stacked body, and a functionalsection provided on the first stacked body and including a nitridesemiconductor. The first stacked body includes a plurality of thirdlayers including AlGaInN and a plurality of fourth layers alternatelystacked with the plurality of third layers and including GaInN. Thesecond stacked body includes a plurality of fifth layers having acomposition different from the composition of the third layer andincluding a nitride semiconductor, and a plurality of sixth layersalternately stacked with the plurality of fifth layers and includingGaInN. The second stacked body includes a first portion near the firstlayer and a second portion located between the first portion and thefunctional section. The In average concentration in the first portion ishigher than the In average concentration in the second portion.

The embodiments are applicable to all the semiconductor devices andwafers having such configurations.

For instance, the embodiments are applicable to various opticalsemiconductor devices such as semiconductor laser devices and lightreceiving devices, current or voltage controlling semiconductor devicessuch as diodes, transistors, field effect transistors, and thyristors,and combinations thereof.

The embodiments can provide a semiconductor device, a wafer, a methodfor manufacturing a semiconductor device, and a method for manufacturinga wafer having high efficiency.

In the description, the “nitride semiconductor” includes semiconductorsof the chemical formula B_(x)In_(y)Al_(z)Ga_(1-x-y-z)N (0≦x≦1, 0≦y≦1,0≦z≦1, x+y+z≦1) of any compositions with the concentrations x, y, and zvaried in the respective ranges. Furthermore, the “nitridesemiconductor” also includes those of the above chemical formula furthercontaining group V elements other than N (nitrogen), those furthercontaining various elements added for controlling various materialproperties such as conductivity type, and those further containingvarious unintended elements.

In the specification of the application, “perpendicular” and “parallel”refer to not only strictly perpendicular and strictly parallel but alsoinclude, for example, the fluctuation due to manufacturing processes,etc. It is sufficient to be substantially perpendicular andsubstantially parallel.

The embodiments of the invention have been described above withreference to examples. However, the embodiments of the invention are notlimited to these examples. For instance, any specific configurations ofvarious components such as the semiconductor layer, light emitting unit,well layer, barrier layer, stacked body, electrode, substrate, bufferlayer, and depression included in the semiconductor device areencompassed within the scope of the invention as long as those skilledin the art can similarly practice the invention and achieve similareffects by suitably selecting such configurations from conventionallyknown ones.

Further, any two or more components of the specific examples may becombined within the extent of technical feasibility and are included inthe scope of the invention to the extent that the purport of theinvention is included.

In addition, those skilled in the art can suitably modify and implementthe semiconductor device, the wafer, the method for manufacturing asemiconductor device, and the method for manufacturing a wafer describedabove in the embodiments of the invention. All the semiconductordevices, the wafers, the methods for manufacturing a semiconductordevice, and the methods for manufacturing a wafer thus modified are alsoencompassed within the scope of the invention as long as they fallwithin the spirit of the invention.

Various other variations and modifications can be conceived by thoseskilled in the art within the spirit of the invention, and it isunderstood that such variations and modifications are also encompassedwithin the scope of the invention.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. A semiconductor device comprising: a first layerof n-type including a nitride semiconductor; a second layer of p-typeincluding a nitride semiconductor; a light emitting unit providedbetween the first layer and the second layer, the light emitting unitincluding a barrier layer and a well layer; and a first stacked bodyprovided between the first layer and the light emitting unit, the firststacked body including: a plurality of third layers including AlGaInN;and a plurality of fourth layers alternately stacked with the pluralityof third layers and including GaInN, the first stacked body having afirst surface facing the light emitting unit, the first stacked bodyhaving a depression provided in the first surface, a part of the lightemitting unit being embedded in at least a part of the depression, and apart of the second layer being disposed on the part of the lightemitting unit embedded in the at least a part of the depression; furthercomprising a dislocation penetrating through the first layer, the firststacked body, the light emitting unit, and the second layer, a sidesurface of the depression surrounds the dislocation, the first stackedbody includes a first region and a second region, a first distancebetween the first region and the dislocation is shorter than a seconddistance between the second region and the dislocation, and a first Alconcentration in the first region is higher than a second Alconcentration in the second region.
 2. The device according to claim 1,wherein the part of the second layer is further embedded in the at leastpart of the depression.
 3. The device according to claim 1, wherein athickness of each of the fourth layers is thinner than a thickness ofthe well layer.
 4. The device according to claim 1, wherein thedepression does not penetrate through the first stacked body.
 5. Thedevice according to claim 1, further comprising: a second stacked bodyprovided between the first layer and the first stacked body, the secondstacked body including: a plurality of fifth layers having a compositiondifferent from a composition of the third layers and including a nitridesemiconductor; and a plurality of sixth layers alternately stacked withthe plurality of fifth layers and including GaInN.
 6. The deviceaccording to claim 5, wherein the plurality of fifth layers include GaN,and a thickness of each of the plurality of fifth layers is thinner thana thickness of the plurality of barrier layers.
 7. The device accordingto claim 5, further comprising: an intermediate layer provided betweenthe first stacked body and the second stacked body and having athickness thinner than a thickness of the light emitting unit.
 8. Thedevice according to claim 1, wherein the well layer includes at leastone of GaInN and AlGaInN.
 9. The device according to claim 1, wherein afirst barrier layer of the plurality of barrier layers nearest to thefirst stacked body includes AlGaInN.
 10. A semiconductor devicecomprising: a first layer of n-type including a nitride semiconductor; asecond layer of p-type including a nitride semiconductor; a lightemitting unit provided between the first layer and the second layer, thelight emitting unit including a barrier layer and a well layer; a firststacked body provided between the first layer and the light emittingunit, the first stacked body including: a plurality of third layersincluding AlGaInN; and a plurality of fourth layers alternately stackedwith the plurality of third layers and including GaInN; and a secondstacked body provided between the first layer and the first stackedbody, the second stacked body including: a plurality of fifth layershaving a composition different from a composition of the third layersand including a nitride semiconductor; and a plurality of sixth layersalternately stacked with the plurality of fifth layers and includingGaInN, the second stacked body including a first portion near the firstlayer and a second portion located between the first portion and thelight emitting unit, and an In average concentration in the firstportion being higher than an In average concentration in the secondportion.
 11. The device according to claim 10, wherein the In averageconcentration in the first portion decreases from a side of the firstlayer toward a side of the second layer, and a variation of the Inaverage concentration in the second portion is smaller than a variationof the In average concentration in the first portion.
 12. The deviceaccording to claim 10, wherein a variation along a direction from thefirst layer toward the second layer of an In average concentration inthe first stacked body is smaller than a variation along the directionof an In average concentration in the second stacked body.
 13. Thedevice according to claim 10, wherein the plurality of fifth layersinclude GaN, and a thickness of each of the plurality of fifth layers isthinner than a thickness of each of the plurality of barrier layers. 14.The device according to claim 10, further comprising: an intermediatelayer provided between the first stacked body and the second stackedbody and having a thickness thinner than a thickness of the lightemitting unit.
 15. The device according to claim 10, wherein the welllayer includes at least one of GaInN and AlGaInN.
 16. The deviceaccording to claim 10, wherein a first barrier layer of the plurality ofbarrier layers nearest to the first stacked body includes AlGaInN.
 17. Awafer comprising: a substrate; a first layer of n-type provided on thesubstrate and including a nitride semiconductor; a first stacked bodyprovided on the first layer, the first stacked body including: aplurality of third layers including AlGaInN; and a plurality of fourthlayers alternately stacked with the plurality of third layers andincluding GaInN; a light emitting unit provided on the first stackedbody, the light emitting unit including a plurality of barrier layersand a well layer provided between the plurality of barrier layers; and asecond layer of p-type provided on the light emitting unit and includinga nitride semiconductor, the first stacked body having a first surfacefacing of the light emitting unit, the first stacked body having adepression provided in the first surface, and a part of the lightemitting unit and a part of the second layer being embedded in at leasta part of the depression; further comprising a dislocation penetratingthrough the first layer, the first stacked body, the light emittingunit, and the second layer, a side surface of the depression surroundsthe dislocation, the first stacked body includes a first region and asecond region, a first distance between the first region and thedislocation is shorter than a second distance between the second regionand the dislocation, and a first Al concentration in the first region ishigher than second Al concentration in the second region.
 18. A wafercomprising: a first layer of n-type including a nitride semiconductor; asecond layer of p-type including a nitride semiconductor; a lightemitting unit provided between the first layer and the second layer, thelight emitting unit including a plurality of barrier layers and a welllayer provided between the plurality of barrier layers; a first stackedbody provided between the first layer and the light emitting unit, thefirst stacked body including: a plurality of third layers includingAlGaInN; and a plurality of fourth layers alternately stacked with theplurality of third layers and including GaInN; and a second stacked bodyprovided between the first layer and the first stacked body, the secondstacked body including: a plurality of fifth layers having a compositiondifferent from a composition of the third layers and including a nitridesemiconductor; and a plurality of sixth layers alternately stacked withthe plurality of fifth layers and including GaInN, the second stackedbody including a first portion near the first layer and a second portionlocated between the first portion and the light emitting unit, and an Inaverage concentration in the first portion being higher than an Inaverage concentration in the second portion.